_ ing. 
OcTOBER 23, 1913 | 
scientific workers give a personal touch to the 
text. We have tried it on a boy of ten and ‘a 
somewhat blasé reader of fifty, and both give the 
same verdict—that it is extraordinarily interest- 
We should like to have seen the authors’ 
names, and we should like to cut the parts and 
bring, let us say, all the Hygiene together; but 
these are minor matters. 
sation all success, because it is sound; and what 
are the factors in this soundness ? 
It appears to us that the chief desiderata in an 
educational enterprise of this sort are the follow- 
ing :—Getting contributors with the gifts and 
graces already alluded to, plus the crowning 
humility of taking pains and obeying the editor 
(to whom our compliments); the good sense not 
to pretend that everything is easy, since nothing 
thorough is; the critical faculty of discerning 
what can be presented accurately, and at the same 
time intelligibly, for while most true ideas are 
clear there is a clarity that only dazzles the man 
in the street; and, last, the restraint which for- 
bids “giving to the ignorant, as a gospel, in the 
name of Science, the rough guesses of yesterday 
that to-morrow should forget.” We do not mean 
to suggest that this huge work has all these 
Virtues in perfection, but it has striven after them, 
and therefore we wish it well. 
OUR BOOKSHELF. 
Arabische Gnomonik. No. 1. By Dr. Carl Schoy. 
Pp. 40+2 plates. Aus dem Archiv der 
Deutschen Seewarte.) (Hamburg, 1913.) 
Tuis mathematical account of Moslem dialling, 
by a writer already known for his studies of 
Arabic astronomy, forms one of the publications 
of the Deutsche Seewarte. 
The author first touches on the bibliography. 
There is food for thought in the fact that but two 
references are given to English writers. The 
Arabic sun-dial differs from that of the Greeks 
in having a single point, at the apex of a spike, 
for index, in place of the gnomon. The horizontal 
dial is first treated, and rules are given for laying 
off “temporary hour-lines.” These hours, duo- 
decimal subdivisions of the daylight interval, vary 
in length; nevertheless, their inconvenience did 
not prevent their universal adoption until the time 
of Abu’l Hassan, who introduced equal hours 
about 1200 A.D. They are specially dealt with in 
the third chapter. The analysis of the clepsydra 
in this chapter gives unequal hours, since it 
assumes—erroneously—a constant rate of dis- 
charge. 
Next follow two chapters on the determination 
of the Kibla and the times of prayer—sunset, 
nightfall, dawn, noon, and afternoon (ast), The 
last, with its various definitions, is discussed in 
some detail. The closing chapters concern verti- 
cal, cylindrical, and conical dials. 
NO. 2295, VOL. 92] 
NATURE 
We wish this populari- : 
231 
Though leaning towards the academic in places 
(the author employs declinations of 36°, — 69°, 
—45°, and 63° on p. 21), the work is of high 
interest and much utility to all who have to do 
with Moslem chronometry. A few typographical 
errors apart, it is well printed, but an index would 
have been a useful addition. Nicgg! Barc: 
Cotton Spinning. By W. S. Taggart. Vol. I. 
Including all Processes up to the End of Card- 
ing. Pp. xxxvi+262. Fourth edition. Vol. I. 
Including the Processes up to the End of Fly- 
frames. Pp. xiv+245. Fifth edition. (London: 
Macmillan and Co., Ltd., 1913.) Price 4s. net 
each. 
THESE books have been brought up to date, and 
much new matter and many illustrations have been 
added. In all essential respects they resemble the 
previous editions, which have gained a wide circu- 
lation among students and practical cotton- 
spinners. 
Modern Problems in Psychiatry. By Prof. 
Translated by Drs. D. Orr 
and R. G. Rows. With a Foreword by 
Sir T. S. Clouston. Pp. vii+305. Second 
edition. (Manchester University Press, 1913.) 
Price 7s. 6d. net. 
Tue first English edition of Prof. Lugaro’s book 
was reviewed in the issue of Nature for January 6, 
1910 (vol. Ixxxii., p. 273). The present issue 
differs in no important respect from the former; 
a large number of minor changes, including the 
correction of several errors, have been made. 
Ernesto Lugaro. 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
The Spectra of Helium and Hydrogen. 
Recently Prof. Fowler (Month. Not. Roy. Astr. 
Soc., December, 1912) has observed a number of new 
lines by passing a condensed discharge through mix- 
tures of hydrogen and helium. Some of these lines 
coincide closely with lines of the series observed by 
Pickering in the spectrum of the star ¢ Puppis, and 
attributed to hydrogen in consequence of its simple 
numerical relation to the ordinary Balmer series. 
Other lines coincide closely with the series predicted 
by Rydberg and denoted as the principal series of the 
hydrogen spectrum. The rest of the new lines show 
a very simple relation to those of the latter series, but 
apparently have no place in Rydberg’s theory. 
From a theory of spectra (Phil. Mag., July, 1913) 
based on Rutherford’s theory of the structure of atoms 
and Planck’s theory of black-radiation, I have been 
led to the assumption that the new lines observed 
by Fowler are not due to hydrogen, but that all the 
lines are due to helium and form a secondary helium 
spectrum exactly analogous to the ordinary hydrogen 
spectrum. This view is supported by recent experi- 
ments of Mr. Evans (Nature, September 4, p. 5), who 
observed the line 4686 in a helium tube not showing 
the ordinary hydrogen lines. Prof. Fowler (Nature, 
September 25, p. 95), on the other hand, brings for- 
