Pathway to Japanese Literature

The Science of Rime Ice

Author: Nakaya Ukichiro

I. The "Monsters" of Mount Zaō

When skiing gained sudden popularity as a winter sport, those who grew dissatisfied with merely playing in practice fields set out further into the snowy mountains.

The allure of winter mountains lies primarily in the solemn grandeur and beauty of their snow.
Those who have once experienced this beauty of winter mountains will never be liberated from it.
Among these people, it was Mount Zaō above all others that came to be extolled for its beauty.

Mount Zaō is a mountain standing 1,841 meters high at the border between Yamagata Prefecture and Miyagi Prefecture.
Whether considering its height or form, it could be called an utterly ordinary mountain with nothing particularly remarkable about it.
At its foothills lie hot springs known as Kaminoyama, Akayu, and Aone.
Also at the summit stands a monument inscribed with a tanka by the poet Mr. Saitō Mokichi, who was born in the Yamagata-facing foothills of this mountain.
And carved upon it is the following poem.

Soaring augustly to split Mutsu asunder, Mount Zaō stands amidst the clouds.

As this poem describes, Mount Zaō indeed divides Mutsu into two parts, with one side facing the Sea of Japan and the other the Pacific Ocean.
Therefore, I shall now explain why this mountain became a holy site for those who pursue winter mountain activities.

Skiers often made a topic of whether they had been to Zaō.
Why did the act of ascending Zaō become such a point of contention among skiers?
The first reason lay in the mountain's severe winter meteorological conditions; while not particularly remarkable in height, the ascent demanded considerable expertise.
Yet this mountain held another, even more captivating quality.
That was the rime ice landscape unique to this mountain.
Mount Zaō's rime ice, now commonly known by the name "monsters," stood arrayed in the snow-clad depths of the mountains with utterly unique visages.

The "monsters" of this snowy mountain had long been known to locals and early winter mountaineers alike, but twelve or thirteen years ago, a German filmmaker came and produced a movie featuring this mountain, introducing it not only across Japan but also widely to the world. Since then, they have suddenly become famous. This rime ice is, to put it simply, coniferous trees entirely covered in snow that have taken on the form of "monsters."

After enduring the grueling climb through blizzards, when one finally reached around the eighth station, they abruptly entered a mystical realm where thousands upon thousands of these monsters stood. As skiers wove through these monsters, gliding freely in all directions, the exhilaration they experienced was something unattainable on any other mountain.

Rime ice was of course not something seen only at Mount Zaō.
In places like Hokkaido, if one ventured slightly into the mountainous areas, it was a phenomenon that could be observed anywhere.
However, it was precisely Mount Zaō's rime ice that stood as the most beautiful and majestic among all known forms of rime ice, a truly worthy representative of this phenomenon.

II. The Phenomenon of Icing

The rime ice of Mount Zaō consisted of snow that had frozen in great quantities onto coniferous trees.
Not limited to Mount Zaō, when venturing into winter mountains anywhere, one often found snow frozen white upon tree branches—though to varying degrees—creating the appearance of beautiful pure-white blossoms in full bloom.
Even at that level, people frequently declared that "the flowers of rime ice had bloomed."
This rime ice differed from freshly fallen snow that lightly settled on branches; it remained frozen fast enough to withstand moderate winds.

However, snowflakes, snow crystals, and similar ice particles do not readily adhere to solid surfaces in the first place.
Even if they collide with considerable force from the wind, they mostly bounce off.
If you strike a fragment of ice against some surface, as becomes immediately clear.
Thus, for snow and ice to freeze onto solid surfaces, there must exist some special reason.
This phenomenon constitutes an extremely important issue in cold countries when considered in broader terms.
And it is generally referred to by the term "icing."

The phenomenon of icing became most problematic in practical terms during snow flight.
When airplanes flew through snow under certain meteorological conditions，this icing formed on the leading edges of wings and propellers，often rendering aircraft incapable of flight.
This had long been an issue even in places like America—so much so that some went so far as to call this icing “the greatest enemy of aviation.”

The Soviet government flew aircraft to the North Pole in 1937—that is, the year when today’s Japan took its first step into misfortune with the Marco Polo Bridge Incident.
The purpose was to transport scholars who would stay on the Arctic ice for one year to conduct polar meteorological observations to the North Pole.
The records of Vodopyanov, the flight commander at that time, were from start to finish a chronicle of how they struggled and fought against this icing.

The terror of icing was not limited to airplanes alone.
The phenomenon of icing on power lines also posed an extremely troublesome problem.
While aircraft icing had ceased to be an immediate concern in Japan at that time, icing on power lines could be said to have grown into an increasingly urgent issue.
This was because during meteorological conditions that caused icing on airplanes, snow would usually freeze onto power lines as well.
And before one’s eyes, the power lines transformed into snow-white serpents.
Buffeted by the blizzard's fierce winds, even the sturdiest power lines would often snap.

The most problematic issue was that high-voltage power lines running from hydroelectric plants to cities frequently fell victim to this calamity. Hydroelectric plants were often located in snow-laden mountainous regions. Therefore, since power lines often ran through snow-laden mountainous regions prone to icing, they were frequently plagued by ice accumulation. As hydroelectric power served as a crucial energy source in Japan at that time, it went without saying that frequent outages—even temporary ones—posed significant challenges. Were railways to become more widely electrified, this problem of icing on power lines would grow increasingly critical.

The study of this critical phenomenon of icing constitutes nothing less than the science of rime ice.
As I previously stated, icing would not occur with snow and ice alone.
The secret of icing in fact resides in the fog accompanying snow.
I shall therefore begin by outlining essential knowledge regarding fog droplets.

III. Freezing of Fog Droplets

Fog consists of numerous extremely small water droplets called fog droplets floating in the air.
Whether we speak of fog droplets or cloud droplets, they are fundamentally the same.
Fog and clouds are essentially identical phenomena—what we call clouds when they exist high in the sky become fog when they descend to ground level.
They are collections of extremely small water droplets.
The fog and clouds we ordinarily observe form when water vapor liquefies into tiny droplets.

Such cloud and fog droplets are often water droplets measuring from one hundredth to five hundredths of a millimeter in diameter. The size of water droplets varies depending on cloud and fog types, and even within the same fog, particles of various sizes intermingle—in any case, they remain small. Among these, those of intermediate size prove comparatively numerous—water droplets measuring approximately three hundredths of a millimeter in diameter. Figure 1 presents a micrograph showing fog droplets captured within an oil film. We designate such dense accumulations of water droplets as either cloud or fog. That said, cirrus clouds appearing like brushstrokes across the highest reaches of blue skies—thin and wispy—consist of small ice crystal clusters, though we shall leave that aside as a separate matter for now.

Figure 1

If clouds and fog are collections of water droplets, let me briefly explain why they do not fall but remain suspended in the air.
They are not truly floating but rather descending extremely slowly; however, their descent speed remains so minuscule that they only appear to float indefinitely.
Just as particles of dust float in the air, the smaller the object, the slower its falling speed becomes due to air resistance.
Even relatively large fog droplets measuring 0.05 millimeters in diameter fall at a mere 26 centimeters per second, and those smaller than this descend far more slowly, creating the illusion of suspension upon casual observation.

Since fog droplets are water droplets, it is only natural that they freeze when adhering to solid surfaces in cold conditions.
And upon closer examination, it becomes clear that rime ice is actually composed of frozen fog droplets.
When peering into the structure of rime ice through a microscope, one finds many formations created by small ice particles frozen together in layers resembling stacked dumplings.
The particles adhere to each other at partial points, so air fills the gaps between them.
Since the particles themselves are grains of ice, they are transparent; however, when such transparent particles accumulate in great numbers, the aggregate appears white like snow.
The reason snow appears white is the same phenomenon: whether crystal or glass, large masses are transparent, but when crushed into powder, they appear white.
This occurs because light is reflected and scattered at the boundaries between particles and the air in the gaps.

Now, in cold environments where icing occurs—places at temperatures like minus eight or ten degrees—a question naturally arises: why do fog droplets remain as water droplets? This occurs because even in such frigid conditions, water droplets can persist in liquid form rather than turning into ice particles. This phenomenon stems from the water being "supercooled."

IV. Supercooled Water

Water may, under certain circumstances, remain unfrozen even below zero degrees Celsius while persisting as liquid.
Such water in this state is called supercooled water.
The thick fog that forms almost daily over winter mountains consists almost entirely of these supercooled fog droplets.

This issue of supercooled water constitutes an extremely significant problem—a phenomenon by no means limited solely to fog droplets.

In elementary school science classes, we are taught that water freezes at zero degrees, but this common explanation proves extremely ambiguous—indeed, it would be more accurate to call it incorrect.
This is because water does not readily freeze even when reaching zero degrees Celsius.

Strictly speaking, zero degrees Celsius is defined as the temperature at which water and ice coexist in a mixed state that persists indefinitely.
When a mixture of water and ice reaches a temperature even slightly above zero degrees Celsius, the ice melts and the proportion of water increases; conversely, when it drops even slightly below zero degrees Celsius, the water freezes and the proportion of ice increases.
It is precisely the temperature at this boundary—neither one nor the other—that constitutes zero degrees Celsius.
Thus, the phenomenon we call "water freezing"—meaning the process by which water turns into ice—refers specifically to instances where this transformation actively progresses. Therefore, unless temperatures fall below zero degrees Celsius, the change of water becoming ice cannot advance.

When water is carefully cooled under ordinary conditions, it never freezes at zero degrees Celsius.
Typically, after being cooled to approximately minus one or two degrees Celsius, ice suddenly begins to form.
By placing distilled water in a test tube, cooling it with salt and snow, and inserting a thoroughly cleaned thermometer inside, one can clearly observe this phenomenon.
The thermometer typically descends to minus two or three degrees.
Eventually, under certain conditions, ice begins to form.
As this happens, the ice gradually grows, and then the water's temperature rises to near zero degrees Celsius.
By "near zero degrees," we mean temperatures extremely close to zero—for example, minus one-tenth of a degree or minus one-twentieth of a degree Celsius.
In this state of remaining extremely close to zero degrees Celsius, over time, the entire mass becomes ice.
The experiment to create this supercooled water is one that anyone can easily perform by keeping the container as clean as possible, using pure distilled water free of dust and other impurities, and cooling it gently.

When water turns into ice, the entire mass does not transform into ice all at once.
A core of ice forms somewhere, and from there, the ice gradually grows.
And then, after a certain amount of time passes, the entire mass becomes ice.
This core substance is referred to as a nucleation site in physics.
When a liquid transforms into a solid—not limited to water but applicable to any liquid—this nucleation site is required.
Even when molten iron solidifies and becomes ordinary iron, the same principle applies—some nucleation site is required.
When water turns into ice, ice fragments serve as the most effective nucleation sites; however, when these are absent, it has been established that dust or container walls fulfill this nucleating role.

Supercooled water could be obtained at considerably low temperatures if one exercised sufficient care in the laboratory.
Supercooling water to around minus ten degrees Celsius was not particularly difficult.

V. Altberg's Research

When we speak of something like supercooled water, it tends to be perceived as an extremely specialized physical phenomenon—something that only physicists need know about.
The phenomenon of water freezing as understood in daily life is often considered a completely distinct laboratory matter bearing no relation whatsoever to ordinary existence.
However, such thinking is profoundly mistaken.
As one example of this misconception, let us here include as an anecdote Altberg's research on the freezing of Siberian rivers.

Siberia was known as an extremely cold and barren wilderness.
However, for the Soviet Union, they could not leave this vast region as barren land.
Therefore, they formulated various plans for Siberian development and implemented them.
Among these was the issue of Siberian electrification.

Siberia possessed a considerable abundance of coal.
However, due to transportation challenges and geographical-climatic conditions, reliance on coal alone for power generation proved impossible.
While water sources for hydroelectricity existed in abundance, these froze during winter months and became unusable in their natural state.
To resolve this dual impasse constituted the fundamental challenge of Siberian electrification.

The scholar entrusted with solving this difficult problem was Altberg.
What did he do first upon receiving this command?
He did not immediately set out for Siberia.

Whether it be Siberian rapids freezing or water in a laboratory vessel freezing, fundamentally they are but a single phenomenon: water turning to ice.
Therefore, he concluded that to solve the problem of river freezing in Siberia, it was first necessary to resolve the fundamental issue of water freezing itself.
When one speaks of something like the problem of water freezing, it might be considered the most commonplace and familiar issue—something that had surely been exhaustively researched long ago.
However, this was an extremely difficult problem, and until then, no one had conducted thorough research on it.

He tackled this formidable problem head-on—astonishingly—shutting himself away in his laboratory for nearly a decade while persisting in relentless study.
Thus he finally solved the problem of water freezing.
The freezing of water always passes through a supercooled state before solidification begins.
In its initial stage, extremely small particles—nucleation sites—first form within the water, after which ice progressively develops.
These nucleation sites form too quickly to be discerned; once established, depending on the degree of supercooling, the entire mass freezes at various relatively slow speeds.
He meticulously examined the crystal formation and development, heat transfer conditions, and quantitative relationships governing freezing progression rates during this process.
This became the first part of Altberg's solution to Siberian electrification—an answer forged through a decade of laboratory life.

Of course, the experiments extended to minute details, but we will not touch upon those here.
After completing this foundational research, Altberg set out for Siberia.
And continuing his research on actual rivers for several more years, he meticulously examined the freezing patterns emerging from the supercooled state of natural river water, ultimately providing a brilliant solution to this problem.
This serves as a clear example of how fundamental research ultimately proves to be the shortest path to victory.

VI. The Formation of Rime Ice

As can be understood from the above account, the phenomenon of supercooled water is the key to solving the problem of freezing.

Now, our subject of study was neither water in containers nor water in rivers.
It was water droplets floating in the air—that is, fog droplets.
In this case, the supercooled state occurred even more readily.
With fog droplets having no container walls to serve as nucleation sites, freezing did not readily occur even when temperatures became extremely low.

The smaller the water droplets became, the more readily supercooling occurred.
In Greenland, Professor Wegener had observed that even at minus thirty degrees Celsius, fog droplets still existed in liquid form.
Furthermore, there were even reports that when American Major Bird conducted his Antarctic expedition, fog droplets remained unfrozen as water in the atmosphere even amidst extreme cold reaching minus forty-four degrees Celsius.

In the low-temperature laboratory, we created water droplets the size of small fog droplets, attached them to fine rabbit hairs, and cooled them while suspended in the air. In such cases as well, we were able to confirm that the water droplets remained unfrozen up to temperatures near minus fifteen to minus seventeen degrees Celsius.

Since fog droplets are considered to be at the same temperature as the air, whenever air temperatures fall below zero degrees Celsius, they invariably become supercooled water droplets.
Supercooled water exists in an unstable state.
When colliding with solid surfaces, they immediately freeze there.
In this case, solid surfaces serve as nucleation sites.
In actual natural conditions, since frost or ice always coats solid surfaces beforehand, supercooled water freezes even more readily through contact with that ice.
This phenomenon of supercooled fog droplets freezing onto solid surfaces constitutes what we call icing or rime ice.

Figure 2

Now, upon closely examining natural rime ice—as previously mentioned—one finds that fog droplets often freeze in layered accumulations resembling stacked dumplings.
This variety has been further classified within rime ice studies; in meteorology it has come to be called soft rime.
However, within rime ice formations there also exists ice that appears less white than soft rime—semi-transparent or nearly transparent.
In natural rime ice conditions this occurs infrequently; but in aircraft icing scenarios it appears regularly and is considered the most hazardous form of icing.
Meteorology refers to this type as hard rime.
Particularly transparent varieties of hard rime are often called blue ice in aviation contexts.
Though soft rime and hard rime represent rime ice's primary forms; naturally occurring icing cannot be neatly divided into these two categories.
There exist of course numerous intermediate gradations between them.

Now, in natural conditions，aside from icing formed solely by such fog droplets，there were cases where snow crystals became mixed in and froze together．When fog capable of causing icing arrived under such conditions，if snow fell mixed within it，the fog droplets acted as glue，causing the snow to freeze onto solid surfaces．

The so-called ice monsters of Mount Zaō—those massive snow formations—are created when dense fog of supercooled water droplets formed off Kinkasan's coast arrives, acts as an adhesive agent, and freezes snow crystals falling on that mountain onto coniferous trees.
With this revelation, the true nature of these mysterious figures had been unveiled.
Mokichi, who wrote of "standing amidst Mount Zaō's clouds," may indeed be said to have masterfully sung of this mountain's distinctive character.

VII. Soft Rime and Hard Rime

The phenomenon of rime ice, in the explanations thus far, becomes merely a simple phenomenon where supercooled fog droplets freeze onto solid surfaces.
Even the icing feared as aviation's greatest global adversary follows this same principle.
This remains fundamentally correct in theory.
The essential question then becomes how such a simple mechanism gives rise to diverse complex icing phenomena.

Earlier, I stated that there were two types of rime ice—soft rime and hard rime—but determining what caused their difference constituted the most crucial question.
However, this difference proved relatively straightforward: when supercooled fog droplets froze onto a solid surface, one could readily imagine there being two distinct freezing processes.
If a fog droplet froze while maintaining its individual form, and then the next droplet adhered and froze on top of it in this upward-layering manner, it became evident that soft rime would form.
However, it was possible for the next fog droplet to arrive before the previous one had completely frozen.
When such occurrences happened to many fog droplets, the solid surface became temporarily coated with a film of water.
If such a water film froze, it would have likely become hard rime similar to ordinary ice.

Thus, ultimately, the problem boils down to two factors: how long a single fog droplet—that is, a supercooled water droplet—takes to freeze, and what time interval exists between successive collisions of fog droplets against a solid surface. We shall designate the former as "freezing time" and the latter as "collision interval." The previous explanation can therefore be restated as follows: when collision intervals exceed freezing times, soft rime forms; conversely, when shorter than freezing times, hard rime forms. This approach of carefully considering phenomena, establishing clearly defined terms, and using those terms to systematically clarify natural processes represents one of science's fundamental methodologies.

First, let us consider freezing time.

Supercooled water is inherently quite unstable.
If there is even a slight stimulus, its stability is immediately disrupted.
Should they contact an ice surface—or any solid surface providing nucleation sites—they would freeze instantly.
Particularly for water droplets measuring 0.03 millimeters in diameter, which typically collide with ice-covered surfaces, one might expect instantaneous freezing.
However, reality introduces the phenomenon that 'water releases latent heat when freezing'—though brief, this means complete droplet solidification requires measurable time.
Thus latent heat becomes integral to understanding freezing time.

The fact that water releases eighty calories of latent heat per gram when freezing is, I believe, taught even in the new junior high school curriculum, but let me provide a proper explanation here.

VIII. Latent Heat

When water freezes into ice, releasing 80 calories of latent heat per gram—to rephrase this phenomenon, water at zero degrees Celsius cannot solidify while retaining this thermal energy; only when 80 calories of heat per gram are extracted from zero-degree water does it transform into zero-degree ice.
The phase transition cannot advance unless precisely this quantity of released heat is removed.

In most cases, when heat is applied to a substance, its temperature rises, and when heat is removed, its temperature falls.
Water and ice also possess this property in the same way.
However, only in the case of water at zero degrees does a special change occur—here, heat does not perform its ostensible action of raising temperature but instead carries out the hidden action of turning solid into liquid.
That is, it becomes latent heat (heat hidden in the shadows).

The concept of latent heat becomes clearer when considering the process of gradually cooling water.
For example, suppose 100 grams of water are placed in a copper cylinder and measured with a thermometer to be 15 degrees.
When this copper cylinder is inserted into a mixture of snow and salt to cool it, the water chills and the thermometer's scale steadily descends.
Since the heat required to change the temperature of one gram of water by one degree is one calorie, if in this case the water temperature decreases at a rate of five degrees per minute, then during that one minute, five hundred calories of heat would be removed from this water and transferred to the salt-and-snow mixture.

In this manner, the water cooled at a roughly uniform rate until reaching zero degrees, but once it reached zero, the thermometer's scale stopped abruptly and would not drop further.
Looking inside the cylinder at that moment revealed ice beginning to form within the water.
Until all the water turned to ice, the thermometer remained at zero degrees; when complete freezing occurred, the temperature began to fall again.
Though considerable time was required for full solidification, it stood to reason that heat continued being drawn toward the snow-salt mixture throughout this period.
Latent heat—unseen on the temperature scale—was being extracted from the water, transforming it into ice.

The amount of latent heat at this time was determined through precise measurements to be 80 calories per gram.
The approximate value becomes clear when conducting an experiment like that shown in Figure 3.
This likely needs no explanation.
To perform this experiment accurately, one must wrap the beaker in cotton for insulation and work swiftly to prevent heat loss.

Figure 3

Reiterating the concept through varied expressions will aid subsequent comprehension.
One gram of water at zero degrees Celsius internally retains 80 calories more heat than one gram of ice at zero degrees.
Removal of this concealed heat transforms water into ice.
Expressed differently: when one gram of water at zero degrees becomes one gram of ice at zero degrees, it releases heat equivalent to raising one gram of water's temperature by eighty degrees.

These matters may be self-evident to those who have studied even a little physics, but for the general reader, I shall provide an explanation that errs on the side of thoroughness.
This is because unless one properly understands this latent heat, they will be unable to fully comprehend the subsequent explanation.

IX. Freezing of Supercooled Water Droplets

When considering how a 1-gram water droplet supercooled to -10°C would freeze upon collision with an ice-covered surface:

The supercooled droplet begins freezing instantaneously at its contact point with the ice surface upon impact. This initiates latent heat release that elevates the droplet's temperature from its initial -10°C state toward 0°C. Upon reaching 0°C, freezing progression ceases entirely as latent heat emission stops—leaving portions of the droplet transformed into ice while residual liquid water remains at equilibrium temperature. This stabilization occurs under our fundamental assumption that no external thermal exchange affects the system.

Figure 4

At this point, it becomes immediately clear that only one-eighth of the entire water droplet freezes and stabilizes.
When one-eighth of a gram of water freezes, ⅛ × 80 = 10 calories of heat are released.
However, these 10 calories represent precisely the amount of heat required to raise a one-gram water droplet that had cooled to -10 degrees Celsius up to 0 degrees Celsius.
Therefore, when a water droplet supercooled to -10°C collides with a solid surface and begins to freeze, one-eighth of its volume becomes ice at 0°C while the remaining seven-eighths becomes water at 0°C, at which point freezing should cease.

In this case—since droplet size proves irrelevant—whether dealing with one-gram masses or microscopic fog droplets, identical proportions undergo freezing.
Consider a supercooled 0.1-gram droplet at -10°C initiating crystallization: any observer would instantly recognize precisely one-eighth solidifying through identical mechanisms.

Suppose there is fog when the temperature is -10 degrees Celsius.
Then, regardless of size, when any of these fog droplets collide with a solid surface, only one-eighth will initially freeze, at which point the freezing process should temporarily cease.
For supercooled water droplets to freeze completely and instantaneously, they must be supercooled to -80 degrees Celsius.
That too should be immediately clear.
However, being supercooled to -80 degrees Celsius is something that does not occur in reality.

When considered in this manner, it becomes clear that whenever fog droplets collide with a surface, a portion of them inevitably remains liquid at the moment of impact. However, this liquid state does not persist long. Since both the external temperature and solid surface remain cold, heat continues to be drawn away into the surrounding environment. Thus, the entire droplet soon freezes completely.

When described in writing this way, one might imagine the phenomenon progresses slowly from collision to complete freezing. Yet this duration is so brief that ordinary language would deem it instantaneous—typically on the order of one-tenth or even one-hundredth of a second. However, such brevity cannot be dismissed with vague terminology; precisely this interval—the freezing time—demands rigorous study. For it is this freezing time that critically governs consequential phenomena like aircraft icing.

X. Freezing Time of Fog Droplets

What determines the freezing time of supercooled fog droplets?
In Figure 4, this water freezes because heat is removed from the portion remaining as zero-degree water to the external environment.
The time required for freezing is therefore determined by the rate at which heat is removed to the external environment.
Consequently, the primary task lies in considering through what means heat is removed from this water droplet.

The first to develop such a theory was the German scholar Brière.
Brière considered two factors: the removal of heat through convection caused by wind, and the loss of heat due to the partial evaporation of moisture.
Subsequently in America, research in this field was taken up as a problem of aircraft icing, and Brière’s theory was further developed.
In Japan, Mr. Ōta Masatsugu of the Central Meteorological Observatory published a detailed study that incorporated heat loss through conduction into Brière’s theory.

First, let me briefly explain Brière’s theory.

The relationship between heat escaping through water evaporation and heat escaping through air convection had been sufficiently studied in thermology for some time.
The fact that both were significantly influenced by wind speed—that is, that increased wind speed resulted in faster cooling—was only natural when considered through common sense.
However, since common sense did not yield quantitative values, physicists undertook to calculate this precisely through physics.

Convection refers to the transfer of heat through the movement of a portion of material that has received heat.
Convection does not occur unless a portion of the material can move freely.
That is, convection occurs only in gases and liquids.
Most gases and liquids are poor conductors of heat when stationary, but when convection occurs, they become good conductors.
Air convection is something we experience daily, and the convection of air in the atmosphere is what we call wind.
The reason it feels cold when wind blows is that heat is carried away through air convection.

When convection occurs, water evaporates.
However, evaporation requires a substantial amount of latent heat.
This latent heat far exceeds that involved in water freezing—approximately 600 calories are needed for one gram of water at 0°C to evaporate into water vapor at the same temperature.
Consequently, even minimal evaporation results in significant heat loss.

By calculating heat removal through both convection and evaporation, Brière theoretically determined the time required for complete droplet freezing.
This freezing duration varies principally according to fog droplet size.
Larger droplets naturally require relatively longer freezing periods, while smaller ones freeze almost immediately.
Wind strength further influences this process through accelerated cooling.
Moreover, lower temperatures enable rapid freezing whereas milder conditions prolong the process.

Incorporating these various factors, Brière theoretically determined the freezing time for each case.
Mr. Ōta incorporated heat lost through conduction into this theory and conducted calculations for various conditions.
Let us examine several examples of these.

Figure 5

When calculated for conditions of -1°C temperature and 10 meters per second wind speed, the freezing time for small fog droplets measuring 0.01 millimeters in diameter came to 0.9 seconds. A diameter of 0.01 millimeters ranks among the smaller sizes found in natural fog capable of causing icing. Under identical meteorological conditions, fog droplets of 0.03 millimeters diameter—the most prevalent size in ordinary cases—were found to require 7.4 seconds for complete freezing. This constitutes a remarkably lengthy duration. However, a temperature of -1°C approaches zero degrees—in low-temperature environments, this would be regarded as exceptionally mild. Consequently, the freezing time lengthened to such proportions.

It goes without saying that if temperatures drop further, freezing occurs far more rapidly. Assuming identical wind speeds of 10 meters per second, calculations indicate fog droplets measuring 0.01 millimeters in diameter freeze within 0.01 seconds at -10°C, while those of 0.03 millimeters require 0.03 seconds.

From these findings, we may conclude that when temperatures fall to approximately -10°C, most fog droplets solidify completely within roughly one-hundredth of a second.

Let us now visualize how rime ice actually forms on mountain peaks.
The wind speed likely measures at least 10 meters per second, with temperatures probably hovering around -10 degrees Celsius.
How then does this relate to the far more critical phenomenon of aircraft icing?
In such cases, since the aircraft moves at tremendous velocity, an extreme wind speed acts upon its airframe.
For an aircraft traveling at 600 km/h, this relative wind speed exceeds 160 meters per second.
Consequently, the freezing time becomes drastically shorter.

XI. Formation of Rime Ice

When supercooled fog droplets collide with a solid surface, a portion freezes instantaneously while the remainder remains in liquid form. After the freezing time has elapsed, it freezes completely. On top of it, more fog droplets freeze, and the same phenomenon repeats. When this process is schematically represented, it appears as shown in Figure 6. (1) Supercooled fog droplets at -10°C collide with a solid surface. (2) Upon collision, almost instantaneously one-eighth of their volume freezes. (3) After the freezing time elapses, the entire droplet freezes. (4) A second droplet collides on top of it and again only a portion freezes. (5) After further freezing time elapses, this droplet also freezes. (6) A third droplet collides and freezes.

Figure 6

The rime ice formed in this manner consisted of small ice particles frozen layer upon layer like stacked dumplings.
This was rime ice, and its overall white appearance was as explained earlier.

The above discussion represented, so to speak, theoretical constructs conceived in the mind.
Whether natural rime ice indeed formed through such a process could not be definitively determined until recent years.
This was because no research involving actual microscopic observation of sites where natural rime ice forms—conducted to confirm this—had been carried out anywhere in the world.

During the war, an icing research institute was established atop a high mountain called Niseko Annupuri in Hokkaido, where we conducted various studies on actual natural icing phenomena.
Through these investigations, we were able to confirm that Brière and others' theories held fundamentally true.

Let me briefly describe the observational process at Niseko Annupuri.

We exposed a thin wire—as fine as a hair—to windy conditions and induced icing on it.
While peering through a microscope, we continuously observed this icing growth process.
Fog droplets then collided with the thin wire.
Upon collision, each droplet's surface initially remained liquid.
This became evident when we saw their surfaces quivering with minute vibrations.
When subsequent droplets struck existing ones before complete freezing, water masses sometimes expanded; however when intervals allowed full solidification between impacts, ice particles accumulated in layered formations resembling stacked dumplings.
Thus rime ice formed.
Watching these delicate ice blossoms develop layer by layer under magnification proved so engrossing we temporarily forgot the bitter cold.

However, the summit of this mountain in winter had meteorological conditions nearly as severe as those of Mount Fuji's summit during winter.
This caused researchers considerable hardship, making prolonged precise observations impossible.
With observations made by tired human eyes, oversights were inevitably numerous.
Therefore, they conducted this research utilizing film.
This involved performing microscopic photography using film.
Then, as the fog droplets collided—initially remaining in a liquid state—their gradual freezing process could be clearly captured.
When they projected this enlargement, they could observe this minute event even more vividly and clearly.

XII. Collision Interval

Now that we have generally understood freezing time as outlined above, next—as previously mentioned—there remains the issue of fog droplet collision intervals.
That is to say, the time between one fog droplet colliding with a solid surface and the arrival of the next droplet constitutes another crucial factor.
Depending on whether this interval is longer or shorter than the freezing time, the structure of the rime ice changes entirely.

Freezing time, as previously mentioned, varies depending on factors such as fog droplet size, temperature, and wind speed, whereas collision intervals differ fundamentally in their determinants.
In this scenario, whether numerous or scarce fog droplets exist in the atmosphere becomes the decisive factor.
With abundant droplets comes rapid successive collisions; scarcity conversely lengthens the interim between impacts.
This makes fog concentration emerge as the paramount variable.

Naturally, wind speed also exerts influence in these conditions.
That heightened wind velocities would compress collision intervals aligns with intuitive expectations.
Physicists substantiated this reasoning through precise calculations determining collision intervals based on fog concentration and wind velocity.

Now, regarding fog concentration, actually measuring this proved difficult.
Taking a fixed volume of fog-laden atmosphere and counting the number of fog droplets within it was possible with contemporary methods, but required somewhat challenging experimental techniques.
Therefore, the best method to obtain a rough estimate became utilizing visibility within the fog.

As any mountaineer knew, when fog thickened, visibility through it became impossible.
In academic terms, visibility decreased.
When climbing a high mountain where skies had been clear moments before, fog would often surge up from below one's feet—rustling audibly, swaying grasses, dampening rocks—transforming the surroundings into a milky-white world almost instantly.
At such times, those dismissing it as mere fog risked losing their way and meeting disaster.
Such dense fog—that with limited visibility—contained greater numbers of fog droplets.
Visibility thus became employed as an indicator for droplet concentration.
Naturally, shorter visibility meant shorter collision intervals.

However， strictly speaking， visibility within fog is not determined solely by the number of fog droplets．
There still remained significant unresolved problems requiring further research； however， at that time， we had no choice but to content ourselves with making rough estimates using this method．
Based on this concept， various scholars calculated collision intervals； among these， let us now examine Mr． Ōta’s calculation example mentioned earlier．

A fog with 50-meter visibility would be considered quite dense. In such conditions, winds blew at 10 meters per second. When calculating the collision interval under these conditions, we obtained a value of 0.27 seconds. This generally became a value roughly comparable in magnitude to the freezing time. If the fog grew denser or the wind speed increased further, this value shortened to about a hundredth of a second. As previously mentioned, whether the collision interval proved longer or shorter than the freezing time significantly altered rime ice's fundamental properties.

XIII. Formation of Hard Rime

Let us once again apply the previous collision interval calculation example.

Visibility 50 meters in fog; wind speed 10 meters per second.

Temperature: -5°C; fog droplets with a diameter of 0.03 mm in ordinary fog.

What form would the rime ice take under these conditions?

When we calculated the collision interval, as previously mentioned, the value obtained was 0.27 seconds.

They calculated the freezing time under these conditions using the previous method.
That value became 0.31 seconds.
In other words，under these meteorological conditions，if things proceed according to theory，it should take 0．31 seconds from when a fog droplet collides with a solid surface until all water droplets have completely frozen．

However, in a shorter time than that—namely 0.27 seconds—the next fog droplet arrives and collides.
This means that before the entire droplet has frozen—while a liquid portion still remains—the next fog droplet arrives.
At this point, it naturally does not form into "flower-viewing dumplings" as in the previous case.
The subsequent droplet adheres to the unfrozen portion of the preceding droplet's water and spreads out over the already frozen ice.
And before it completely freezes, the next droplet comes flying again.
In this manner, the phenomenon progresses.

In such cases, the solid's surface remains perpetually covered by a water film that freezes sequentially.
The ice formed through this process becomes nearly transparent—what we call hard rime.
When I previously stated that "hard rime forms when freezing time exceeds collision interval," this was precisely the scenario I described.

A model depiction of the process by which this hard rime forms is shown in Figure 7.
To align with the example in Figure 6, let us examine the case where supercooling reaches -10 degrees.
(1) Supercooled fog droplets cooled to -10 degrees collide with a solid surface. (2) One-eighth freezes instantly upon collision. (3) Before the remaining water has fully frozen, the next fog droplet collides. (4) A water film at 0 degrees spreads out. (5) Freezing progresses while the surface remains covered by this 0-degree water film.

Figure 7

This state was also observed under a microscope at the Niseko Annupuri observatory and captured even more effectively on film.
In some cases, water droplets took a surprisingly long time to freeze.
Therefore, the water droplets gradually grew larger as they remained.
And there were cases where, upon reaching a certain size, they suddenly began freezing from the inside.

In this manner, it became clear that what had been discussed thus far was generally correct in principle.
However, rime ice observed in nature formed through an extremely complex process.
Conditions conducive to soft rime and those leading to hard rime intermingling were actually more common.
Moreover, there were cases where the phenomenon of sublimation—something we had not considered at all until now—also came into play.
Sublimation refers to the phenomenon where ice transforms directly into water vapor without passing through the liquid state, or where water vapor transforms directly into ice.
The ice formed through this sublimation was crystalline ice, entirely distinct from the types of ice discussed thus far.
Furthermore, to Mount Zaō's "monsters," another phenomenon was added—one where snow crystals became mixed in and froze together.
It became abundantly clear that explaining rime ice merely as snow clinging to trees would render the explanation utterly meaningless.

XIV. Aircraft and Icing

The science of rime ice is, in other words, the science of icing.
Whether we speak of rime ice or icing, they are fundamentally the same phenomenon; it is called rime ice when adhering to natural trees, while the term icing is conventionally applied when it forms on aircraft wings or window panes.

One must not dismiss inquiries into how Mount Zaō's rime ice forms as serving no purpose.
The science that overcomes the "aviation industry's greatest enemy" worldwide is none other than the science of rime ice.

Rime ice itself constitutes an extremely complex phenomenon as discussed thus far.
However, when it comes to icing on aircraft, the matter grows even more troublesome.
Aircraft must navigate through various complex meteorological conditions, and due to their significantly high speeds, the phenomenon becomes still more challenging.

However, when examining aircraft icing through its fundamental mechanisms, the aforementioned theoretical framework proves provisionally adequate.
Let us recapitulate and systematize these findings.

The occurrence of icing conditions proves primarily contingent upon temperature.
Moreover, as factors like freezing duration fall entirely under wind speed's governance, velocity emerges as a critical parameter in aviation contexts.
The abundance of fog droplets—that is to say, fog density—likewise constitutes a determinant factor.

Thus, while various conditions each exerted their influence, they did not necessarily act independently.
Among these factors, in aircraft icing cases, temperature had traditionally been regarded as the most critical issue.
Even when examining various actual instances where icing occurred during flight, it was known that icing most readily occurred between approximately -1°C to -2°C and -8°C.
When temperatures dropped below that range, icing was paradoxically considered less likely to occur.
However, records existed in American scheduled aviation where icing had occurred at temperatures as low as around minus twenty degrees, making this a relative matter.
When temperatures became too cold, not only did the amount of supercooled water droplets decrease, but icing also rarely occurred due to other unconfirmed causes.
The most dangerous meteorological conditions had come to be thought as those ranging from near zero degrees to around minus eight degrees, with thick fog during such periods considered most hazardous.

However, in recent times—though 'recent' here refers to the wartime period—research on icing advanced, and the influence of wind speed (i.e., aircraft speed) gradually came to be understood.
That had a significant impact indeed.
Then, for aviators, this became an extremely troublesome problem.
Before an airplane takes off, only natural wind blows on objects on the ground.
Therefore, the conditions there are such that icing does not occur.
If one thought this way and took off, icing would occur only on the aircraft.
Such most adverse conditions could indeed occur, and when they did, one had to exercise extreme caution.

The issue of wind presented a significant challenge, but the reason it had not been extensively studied until recently was that conducting experiments proved difficult.
This research required a wind tunnel capable of directly ingesting atmospheric conditions conducive to icing—what was termed an icing wind tunnel.
The optimal method was to install such a wind tunnel at the summit of a high mountain where icing conditions persisted almost daily throughout winter and conduct experiments within it.

There was also a method where, for similar purposes, one constructed a wind tunnel within a low-temperature chamber and attempted to induce icing by spraying fog droplets into it using a mist sprayer.
Such methods had been attempted in foreign countries for over ten years.
However, even then they still did not truly understand the matter, and it went without saying that using atmospheric conditions in their natural state of icing was far superior.

Having reached this point, one could understand how profoundly challenging the study of icing—that is, rime ice—truly was, and how it demanded large-scale facilities.
One could comprehend how even something as commonplace as rime ice—utterly unremarkable to skiers—presented such formidable obstacles in genuinely unraveling its secrets.

XV. Fog Droplets and Airflow

Through the above research, we gained a considerable variety of knowledge regarding icing.
However, problems still remain.
This is because the research conducted thus far has primarily been studies on icing from the perspective of thermodynamics.
However, to grasp the true nature of icing，it becomes necessary to also focus on aspects of airflow beyond what has been discussed thus far.
In other words，fluid dynamics research also emerges as one important subject.

To discuss these problems systematically by separating them one by one，until now we had simply described how fog droplets collide with solid surfaces and freeze upon impact.
However，when fog droplets are carried by wind currents，we must examine whether they actually collide with solid surfaces as straightforwardly as posited.
Needless to say，if fog droplets were indeed flowing perfectly synchronized with air currents，they should theoretically never collide with solid surfaces.

Now, suppose there is a single round pillar.
The circle in the center of Figure 8 shows the cross-section of this pillar.
If we assume the wind is blowing from the right, the air splits into upper and lower streams at the pillar as indicated by the thin lines in the figure, flowing around it.
If the fog droplets were completely carried by the airflow, they should flow around the pillar as seen in the diagram.
If this were so, then on the solid surface—in this case, the cylinder's surface—the fog droplets would not collide at all.

Figure 8

However, in reality, fog droplets collide with the pillar and adhere.
This occurs because fog droplets do not move entirely in accordance with airflow.
A clear example manifests when sand blows about.
When walking a road on a windy day, wind naturally strikes one's face.
The air then flows around the face and streams backward.
Yet sand dust stirred by this wind—particles remaining airborne briefly—behaves precisely like fog droplets.
This sand dust approaches our faces, collides with them, with some particles flying into eyes.
Such phenomena form part of daily experience.
Herein lies proof that sand particles are not fully carried by wind currents.
While air flows around facial contours, sand grains fly straight toward eyes.
Extremely fine particles nearly follow airflow completely, but larger ones—owing to their motion's inertia—readily deviate from air current paths to fly straight ahead.

When fog droplets carried by wind collided with a solid surface, if they had been as heavy as sand particles, all fog across the solid's entire surface would have frozen solid.
If they were extremely light, most would flow around the solid, and icing would hardly occur.

In the case of an airplane, since its wings were shaped to minimize air resistance, the air split cleanly above and below them and flowed backward.
Therefore, if fog droplets had been extremely light and completely followed the airflow, no matter how numerous they might have been, they would all have flowed around aircraft wings following the same distribution pattern as the airflow.
Thus, the phenomenon of icing on aircraft would not have occurred.
However, since fog droplets had considerable weight, some were deflected and flowed away while others collided with wings and froze.
What percentage of all fog droplets present on an object's front surface would end up freezing?
That was determined by both the weight of the fog droplets and the size of the object they froze onto, so let us examine this quantity.

XVI. Capture Rate

Considering airplane wings made the problem exceedingly complex. To simplify our analysis, we turned instead to examining a cylindrical pillar. We then modeled airflow containing fog droplets approaching directly toward its frontal surface.

Figure 9(a) showed the case where fog droplets were heavy.
In other words, using the previous example for comparison, this corresponded to when sand particles would fly into one’s eyes.
The thick solid lines in the diagram depicted the airflow, while the thin lines indicated the movement of fog droplets.
At points distant from the pillar, air flowed uniformly in parallel, but upon approaching the pillar’s vicinity, it divided into upper and lower streams around the pillar, causing the flow path to curve as shown in this diagram.
However, since fog droplets were heavy, their motion possessed significant inertia; even as they approached the pillar, they continued moving straight along their original trajectory—in other words, flying directly ahead—and collided with the pillar.
In this case, all fog droplets present on the pillar’s front surface ended up colliding with it.

Figure 9

Part (b) of the same figure showed the case where fog droplets were extremely light.
In this scenario, since the fog droplets were completely carried by the airflow, they all diverted along the same path as the air currents flowing around the pillar.
Under these conditions, icing did not occur at all.

In case (a), all fog droplets present across the pillar's frontal surface collided with it, while in case (b), none made contact.
These two cases represented extreme opposites; in reality, as previously explained, an intermediate phenomenon manifested.
Part (c) of the same figure illustrated this transitional state.
Here, a certain proportion of fog droplets from the pillar's frontal area pierced through the airflow stream to collide with the structure.

If this collision ratio could be quantitatively calculated in advance, it would prove extremely advantageous.
This numerical value indicating the ratio is called the capture rate.
In the case of Figure 9(a), this capture rate means all droplets are captured—that is, one.
In case (b), since none are captured, it is zero.
In natural conditions where icing actually occurs, the capture rate becomes an intermediate value between one and zero—for example, 0.2 or 0.6.
That numerical value is determined by the size of the fog droplets, wind speed, and the size of the object.

Theoretical studies on capture rates had also been conducted by scholars from various countries for some time.
In Japan, these calculations were conducted by Mr. Imai Ichirō of the Central Meteorological Observatory.
The method involved fluid dynamic calculations, and through these, the following insights were obtained.
In other words, the capture rate gradually increased as wind speed rose, and of course changed if the size of the fog droplets differed.
Moreover, another crucial factor was that as the pillar thickened, the capture rate decreased.

Let us present an example of Mr. Imai's calculations.
When calculated for an object the size of an aircraft wing—with fog droplets 0.01mm in diameter and a wind speed of 30 meters per second—the capture rate came out to approximately 0.1.
In other words, approximately 10 percent of the fog droplets present on the wing's front surface collided with it and formed ice.

However, under identical meteorological conditions—0.01mm fog droplets at 30m/s wind speed—the capture rate increased significantly for smaller objects.
For instance, when examining something as slender as a power line, the capture rate reached approximately 0.9.
This meant nearly 90 percent of fog droplets across the frontal area corresponding to the power line's thickness froze onto that line.

Of course, these 0.1 and 0.9 concern 'rates'. On the front surface of large objects like airplane wings, there exists an enormous number of fog droplets, with one-tenth freezing onto them. For something as thin as a power line, while fewer fog droplets exist across its front surface, nine-tenths freeze onto it. Naturally, the actual quantity of fog droplets that freeze proves far greater on aircraft wings than on objects like power lines.

Once capture rates become understood, one can estimate how rapidly icing might advance under specific meteorological conditions. In aircraft cases, minor icing poses no danger but turns hazardous when exceeding a certain threshold. When dealing with an icing-inducing cloud layer of limited thickness—say one an aircraft could traverse within one minute at speed—we must assess whether dangerous ice accumulation would occur during that minute. To make this judgment requires knowing the capture rate's value, even if only roughly approximated.

Regarding icing on power lines too, the amounts freezing onto thick transmission lines and cables versus those forming on thin wires like telephone lines did not maintain proportional ratios. For instance, a wire one-tenth the thickness of its thicker counterpart did not accumulate one-tenth the ice quantity, but rather froze a significantly greater amount. Such findings needed to serve as foundational reference material when considering methods to prevent or remove icing on power lines.

XVII. The Shape of Icing

To experimentally verify the theory of capture rate，experiments were conducted in various locations．
In our country as well，studies were conducted at locations such as Mount Fuji，Mount Zaō，and Niseko Annupuri．
However，this experiment was extremely difficult．
Or rather，the theory itself was severely divorced from reality．
The basis of the calculation lies in the form of airflow around a cylinder．
Thus，while this theory applies up until the moment icing occurs，once ice growth progresses slightly，the cross-sectional shape becomes that of a cylinder with accumulated ice．
It cannot by any stretch be called circular．
Therefore，this theory is applicable only up to where icing has formed a very thin surface layer．
As for icing of this degree，experimental results showed that this theory generally holds true．
However，what happens when icing has grown considerably—such as reaching the state shown in Figure 10？
In truth，this latter case was more critical；while experiments had been conducted on such instances，theoretical understanding had made almost no progress．

Figure 10

The conventional understanding of capture rates had been based on the assumption that airflow was uniform.
However, in natural icing conditions, the airflow was never uniform.
In most cases, when a solid obstruction existed, numerous small vortices formed in the surrounding air.
And the shape of icing was significantly influenced by those vortices.

There had long been numerous records detailing the forms of icing that naturally developed on tree branches and similar surfaces. Most exhibited fine striated grooves with uneven textures as illustrated in Figure 10. Skiers observing rime ice formations in winter mountains would find their shapes—barring exceptional cases like Mount Zaō's ice monsters—largely conforming to this Figure 10 pattern. As previously noted, this striated structure was understood to form through aligned vortices within airflow patterns. Nevertheless, comprehensive studies elucidating these mechanisms remained absent.

Incidentally, let us note another type of icing included within rime ice in the broader sense.
This is what is called sublimation frost.
Sublimation frost is rarely seen and moreover does not develop significantly, so many people fail to notice it.
This forms when water vapor directly turns into ice crystals through sublimation, and in terms of formation process, it is identical to snow crystals.
Snow crystals are formed when water vapor in the sky condenses around fine dust particles floating in the air—particles so minute they remain invisible even under a microscope.
Through the same process, when water vapor condenses on the surface of tree branches and forms ice crystals, this constitutes sublimation frost.

Sublimation frost can occasionally be observed in high mountains during the severest cold, on mornings following windless, quiet nights.
It consists of brittle crystalline ice that extends abundantly from tree branches into the air.
However, if the sun shines, it soon evaporates, and if the wind blows, it breaks and falls off, so by afternoon it has often already disappeared.
This has no relation to fog droplets and therefore does not possess the property of "freezing onto surfaces."

XVIII. Conclusion

On a clear winter mountain morning, against a sky so clear it appeared indigo, every branch on the mountain bloomed with pristine white rime ice flowers. The air was cold, but with no wind and the sun shining, it wasn’t unexpectedly cold. Or rather, it was a refreshingly pleasant cold. A world of silver-white stretched as far as the eye could see. Not a trace of human presence remained. What rendered the silent winter mountain even more silent was the rime ice flowers blooming across every branch. Anyone who saw this scenery would never forget its beauty for the rest of their lives.

When a blizzard struck, the winter mountain transformed its visage in an instant.
Ice fragments mixed with snow scattered like gravel, making it impossible to lift one's face.
It became a white-night darkness where even five meters ahead could not be seen.
Along with the roaring wind, that white-night darkness thickened and thinned moment by moment.
With each gust, the blizzard waxed and waned.
The skiers desperately tried to seize gaps in the wind to gain visibility.
In that instant, visibility abruptly cleared.
What entered their field of vision was the sight of monstrous snow-clad mountain figures jostling against each other beneath an ashen sky.
None of this belonged to the human realm.
The uncanny impression received in such moments would remain etched in the depths of one's mind for a lifetime.

The beauty of rime ice, its uncanny allure—these will not be eradicated by scientific progress. However, this does not mean that rime ice ceases to be a subject of scientific inquiry. If even the scientific knowledge of rime ice written in this text comes to be properly understood, the next winter mountains' rime ice will likely appear still more beautiful and still more mysterious.

To explain merely how snow freezes onto trees required this many pages.
Some readers may have been slightly taken aback.
However, the science of rime ice remains only at the threshold.
Researchers have thus far advanced model-based approaches for extremely simple cases and solved them mathematically.
As for experimental research, it had only preliminarily confirmed these theoretical conclusions and progressed just slightly beyond that.

Scientists will continue their research on rime ice in the years to come.
And from that research, they will devise methods to vanquish "the aviation industry’s greatest enemy."
Moreover, it will eventually become possible to completely protect power lines—the lifelines of civilization—from the ravages of snow.

If one were to dismiss rime ice as merely snow frozen to trees, that would be the end of it. However, even that simple matter—if one attempts to elucidate it scientifically—how profoundly difficult it proves would have been well understood through this text's explanations.

Not limited to rime ice, nearly all phenomena occurring in the natural world present an extraordinary challenge when one attempts to truly elucidate them scientifically.
Nature, as an entity, is inherently profoundly deep and harbors infinite mysteries within its depths; this is only to be expected.

However, precisely because of this, even a phenomenon considered utterly commonplace—if it becomes truly scientifically elucidated—there is no mistake in thinking that practical effects will emerge in unexpected places.
Research on rime ice is but one example of this.
(March 1950)