Table Of ContentSnow Crystals: Natural and Artificial
Snow Crystals
NATURAL AND ARTIFICIAL
Ukichiro Nakaya
HARVARD UNIVERSITY PRESS - CAMBRIDGE • 1954
COPYRIGHT 1954 BY THE PRESIDENT AND FELLOWS OF HARVARD COLLEGE
DISTRIBUTED IN GREAT BRITAIN BY
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Preface
When the Faculty of Science was established at Hokkaido University, Sapporo,
Japan, in April 1930, I was offered and accepted a position in the Department of
Physics and immediately took up residence in Sapporo. My experiences during two
snowy winters in Sapporo led to the idea of conducting physical investigations on
snow, and I began the study of snow crystals toward the end of 1932 as my first
project in the field of snow investigation.
I spent the first winter in taking photomicrographs of snow crystals at our Uni-
versity laboratory in Sapporo. During the next few winters I changed my place of
study to the Hakugin-sö (Silvery Villa), a dormitory of forest guards of the Hokkaido
Prefectural Office. The villa was located at a height of 1030 m above sea level on a
slope of Mount Tokachi, near the center of the main island of Hokkaido. During
three winters there, I endeavored to gather as many photomicrographs of various
kinds of crystals as possible. In the observations carried out during the first two
winters, we found numerous varieties of snow crystals — not only every type thus
far reported, but also some crystals hitherto quite unknown in the literature. We
were therefore able to make a general classification of snow crystals which was
extremely broad in its coverage.
In parallel with these observations at Mount Tokachi, the work of taking photo-
micrographs of crystals at Sapporo was also continued. Later we spent two winters
at a mountain hut located on a slope of Mount Asari near Sapporo. Photographs of
crystals taken at this spot added considerably to our collection of crystal pictures.
I was ill at the time, and Professors Seiji Kaya and Jumpei Harada, two of my col-
leagues, took my place in directing the observation squad sent to the hut. I express
my gratitude here to these professors.
In addition to the work on a general classification scheme, we commenced (in
1934) the study of the physical nature of each type of crystal. This undertaking,
chiefly conducted at Mount Tokachi, included measurements of the mass and
velocity of fall of individual crystals, for the purpose of finding the relation between
these quantities and the size and form of crystals. The electrical nature of each snow
vi PREFACE
particle was also studied. Lastly, the frequency of occurrence of each crystal form
was studied, the observations for this purpose being carried out for a whole winter.
These observations indicate that plane crystals of hexagonal symmetry, which have
been believed to be the representative form of snow crystals, constitute only a small
part of natural snow crystals and that in actuality irregular types of crystals are more
abundant.
These studies constituted the first part of our investigations on snow. The results
obtained were comprehensive, but we could not as yet begin to explain the simplest
and most primary problem, why snow crystals show such a complicated variation
in form and structure. With regard to this problem, many studies had been made in
Europe and America on the relation between crystal forms and meteorological con-
ditions. We also worked on this subject in Hokkaido. However, inasmuch as the
snow crystals are formed high up in the atmosphere and meteorological conditions
usually recorded are the results of observations on the surface of the earth, we could
not expect any simple relation between them. As we had anticipated, the actual
observations yielded little or no pertinent information.
It was felt that a solution of this problem should be obtainable by producing
these crystals artificially in the laboratory. Thus, by studying the relation between
the crystal form and the conditions Under which it is formed, the basic question
could be answered unambiguously. However, we could not foresee the difficulties
that lay before us in solving this problem, since no work on the artificial production
of snow crystals had been reported at that time. So a beginning was made with the
artificial production of frost crystals. The form and structure of frost crystals may
be regarded as very similar to those of a single branch of a snow crystal, some forms
of frost crystals corresponding to those of snow. Hence, the conditions of snow
formation may be inferred, to some extent, on the basis of the knowledge acquired
in producing various types of frost crystals.
Even the early experiments on the artificial production of frost proceeded
smoothly and yielded useful data, but it was natural that the crystals of frost which
developed on the cooled surfaces of solid bodies were in various ways different
from snow crystals formed afloat in the air.
At about this time, construction of the Low Temperature Laboratory was begun
at Hokkaido University; the new laboratory was completed in February 1936. The
experiments on the artificial production of frost were moved into the cold chamber
of the new laboratory, in which the temperature was usually kept at -35°C. In this
chamber we found that we could produce frost crystals without using a cooling sur-
face. Soon thereafter, owing to the improvement in equipment, we succeeded in
producing ice crystals afloat in the air — in other words, snow crystals — by making
an ice crystal develop on a point of thin rabbit hair.
Since then, our studies on the artificial production of snow crystals have been
PREFACE vii
continued, and it is felt that the basic problem is nearing complete solution. Today
we can produce every type of natural snow crystal in the laboratory, and the condi-
tions of their formation have been determined in almost all cases.
September 1946 U. NAKAYA
Four years have already elapsed since I finished the last page of the manuscript
of the Japanese edition of this book. Meanwhile, the printing work was making slow
but steady progress under the adverse conditions of the War, when unfortunately
the printing office was bombed and the whole copper type and original type of the
text were burnt. At that time it was impossible to reset the type and I gave up hope
of publication.
In the early spring of 1949, I was greatly encouraged by Dr. H. C. Kelly of
the Economic and Scientific Section, GHQ, SCAP, to again prepare the photographs
for publication. The authorities at Hokkaido University also rendered assistance by
making available a special research fund. Nothing surpasses the author's happiness
as he looks forward to the birth of this book from a copy of the proof which survived
the war. Its publication has been made possible by the kindness and sympathy of
various persons, especially by the courtesy of Dr. Charles F. Brooks, Director of
Blue Hill Meteorological Observatory, Harvard University, and of Dr. B. C. Dees
of the Economic and Scientific Section, GHQ, SCAP, who gave much advice on the
preparation of this English edition. The author is also much indebted to Mr. Harold
M. Lane, who took the trouble to read through the manuscript. The most sincere
gratitude is expressed to the American Academy of Arts and Sciences, which made
the grant of $1500 from The Permanent Science Fund necessary to supplement
the funds that the Harvard University Press was in a position to allocate to the
manufacture of this book, and to Dr. Brooks, by whose kind assistance this grant
was obtained. Although the progress of research during the past few years might
make advisable additions or deletions in some places, the author decided to present
the book in the form of 1946, being afraid of losing the opportunity again. Never-
theless, the last chapter summarizes the recent research in cloud physics, including
work done in our laboratory.
February 1953 U. NAKAYA
A cknowledgments
This work was accomplished by the cooperation of staff personnel of my divi-
sion in the Department of Physics, Hokkaido University, as well as of undergraduate
students who did their undergraduate research theses under my charge.
The author takes this opportunity to express his thanks to Assistant Professors
Toichi Terada and Masando Hanajima, to Messrs. Tamakichi Takano and Ikuzo
Kagami, who worked with him for many years under the terrible chill, and to Messrs.
Tsuneo Iijima, Katsuji Hashikura, Isonosuke Satö, Yataro Sekido, Motoichi Tada,
Yasuaki Toda, Shuzo Maruyama, Yasushi Sumi, Shun Inada, Yukio Miyazaki,
Hiroshi Endo, and Chöji Magono, who undertook parts of the work as their
graduation experiments.
The success in the most difficult experiments in the latter half of the study on
artificial snow is especially due to the efforts of Assistant Professor Hanajima, who
continued the experiments for many years in the low-temperature room. The author
herewith presents his thanks and expresses his admiration for the persistent exertion
of this splendid colleague.
This series of researches was aided by the Education Ministry subsidy for sci-
entific research and by grants from the Japan Society for Promotion of Scientific
Research and from the Hattorf Hökökai. In addition, the progress of our study owes
much to the benevolence of Mr. Köichi Hanajima. Herewith I express my hearty
thanks to these contributors.
