73 NATURE 

attempt, only 300 tons of iron were produced in seven 
years at a cost of 50,000]. A study of the entire 
book shows that at the moment barytes is practically 
the only mineral of serious economic importance that 
Treland is capable of producing. Apart, however, from 
the strictly commercial aspect of the subject, Prof. 
Cole’s work is of great value to the student of mineral 
deposits, inasmuch as it supplies authentic information 
concerning the mineral resources of the country. 
Overzicht van de theorie en de toepassingen van gassen, 
waarin de onderlinge botsingen der moleculen kunnen 
verwaarloosd worden. Door Dr. Jos. ter Heerdt. 
Pp. vii+324. (Utrecht and Nijmegen: N. V. 
Dekker & Van de Vegt en J. W. van Leeuwen, 
1923.) 6.50 florins. 
Since the classic researches of Maxwell on the 
internal friction of gases and those of Crookes on 
radiometer theory, no investigations have been so im- 
portant in connexion with the kinetic theory of gases 
as the work of Martin Knudsen on the properties of 
highly rarefied gases, in which the mutual collisions of 
the molecules may be neglected. Dr. Jos. ter Heerdt 
has produced a very clear monograph in which the 
work of Knudsen and that of some other investigators, 
Soddy and Berry, Gaede, Langmuir, Weber, etc. 
(scattered in many periodicals), is brought together 
and critically discussed. 
After a short historical introduction and some general 
considerations regarding the kinetic theory of gases, 
(Chap. I.), the author deals in the following chapters 
with molecular flow through narrow capillaries and 
small holes in plates, with molecular flow through tubes 
with a temperature gradient (pressure equilibrium 
between two reservoirs at different temperatures, con- 
nected by a capillary tube), with the molecular con- 
duction of heat and the coefficient of accommodation. 
The treatment of the problem of accommodation, as 
given in Chap. VI., is new and throws a new light on 
the question. Nevertheless no general solution is given 
of this very complicated problem. Chap. V. deals with | 
the radiometer force and with the formula which 
Knudsen has deduced for it. In Chap. VII. a full and 
detailed description is given of modern high yacuum 
pumps, based on the principles of the kinetic theory 
of rarefied gases (Gaede, Langmuir) and of different 
kinds of high vacuum manometers. 
with a very complete bibliography. 
The volume forms a readable and clearly written 
monograph on a subject not covered by any existing 
work and may be highly recommended to all who are 
interested in this subject. It is to be hoped that the 
book, which is published in Dutch, will be translated 
into English, French or German in order that it may 
reach a wider circle of readers. C. A. CROMMELIN. 
Hawatki: the Original Home of the Maori. 
Sketch of Polynesian History. By S. Perey Smith. 
Fourth edition. Pp. 288+20 plates. (Auckland, 
Melbourne and London: Whitcombe and Tombs, 
Ltd., 1921.) ras: 6d. 
It is most fortunate that Mr. Percy Smith was able to 
publish the fourth and authoritative edition of this 
book before his death, as it contains a considerable 
amount of new material and of revised conclusions. 
NO. 2796, VOL. 111 | 
The book ends | 
With a | 

' expressionism would result in an absolute rejection — 
| work a number of infantile characteristics. : 
attempting to understand the external world, they — 
[JUNE 2, 1923 
It represents the gleaning of a long life spent in amassing 
new data, and laboriously sifting and collating existing 
information. All students of oceanic ethnology owe 
a great debt to this painstaking, kindly, and learned 
pioneer. Mr. Smith entirely justifies his reliance on 
the general accuracy of tradition, and he has been able 
to give approximate dates to events in unwritten 
history, and also to trace three main migrations into 
the Pacific from Indonesia, and numerous migrations 
within the Polynesian area. Constructive work of 
this kind on imperfect material is necessarily open- 
to criticism, but Mr. Smith courageously attempts to 
interpret hints and obscure words, and by imagination, 
controlled by intimate knowledge of Polynesian — 
ethnology, he has made a plausible connected story, 
which, in his concluding words, “ will in the meantime 
serve the purpose of a summary of the history of the 
people, on which others may build.” 
The Indian dates on p. 85 require revision. The 
Saka entered the Panjab about 75 B.C., not 950 B.C. ; 
the great colonisations of Java from India are also 
placed much too early; according to Havell they 
were due to the final collapse of the Saka power at the 
beginning of the fifth century. It is important to 
have correct dates for events in India, as Mr. Smith 
uses them in the development of his thesis. The view 
that the Polynesians may have been in part a branch 
of the “‘ ancient Gangetic race’’ has much to recom- 
mend it, but by terming them “ Proto-Aryan” he 
raises very grave difficulties, but, perhaps, Pre-Aryan 
is what he meant to express. 
This little book is invaluable to all those who take 
an interest in the history of the most intrepid explorers 
of the Pacific. A. C. Happon. 
Expressionism in Art: Its Psychological and Biological 
Basis. By Dr. Oskar Pfister. Authorised trans- 
lation by Barbara Low and Dr. M. A. Mugge. Pp. 
viliit272. (London: Kegan Paul and Co., Ltd., 
1922.) 6s. 6d. net. 
Dr. Prister’s work is a study by psycho-analytic 
methods of a French artist suffering from depression, 
who came to the author for psychological treatment. 
In addition to the analysis of his dreams, the artist 
was asked to draw whatever he liked, and these draw- 
ings, usually of an extremely unconventional character, 
were treated in the same way as the dreams. The 
results are very interesting, both from the insight 
obtained into the personality of the artist and also 
from the light thrown on that type of art generally 
known as expressionism. 
The first part of the book is a study from a psycho- 
logical point ‘of view of the artist ; the second part 
discusses the psychological and biological background 
of expressionism. The author shows how excellent 
for diagnostic purposes were the pictures which in- 
variably represented the artist’s psychical state. 
From a study of the pictures of other expressionists, — 
he concludes that all expressionists carry into their 
Instead of 
turn away and represent their own internal conflicts 
in phantasy form, their pictures thus being in reality 
self-portraits. If pushed to its logical extremes, 
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