274 
In a new edition pages 18, 19 and 20, in so 
far as they discuss air density, might be 
slightly modified to advantage. Here “air 
holes” are spoken of as places of low air den- 
sity. 
An aeroplane entering one of these low density 
regions from the air of higher density around it, 
will suddenly fall without any warning, merely 
because the pressure has enormously decreased, 
and the aeroplane has not had time to attain the 
requisite velocity of support in this lighter medium. 
Enormous differences 
cause enormous changes in the barometer, but 
such sudden changes are never found in the 
open, and, besides, it can be shown that the 
movement (whirl) of the atmosphere neces- 
sary to produce a change of pressure amount- 
ing to one tenth of the total would be of most 
destructive violence. 
But this is a small fault to find with a book 
so generally helpful. 
Elementary Aeronautics. By Apert P. 
Tuurston. Whittaker and Co., 126. 
This is a non-mathematical but clearly 
written account of the action of air upon 
moving surfaces, plane and curved, and the 
application of these principles in the design 
and operation of aeroplanes. 
While both elementary and brief, it seems 
to be free from errors, and can be recom- 
mended to those who wish some reliable infor- 
mation about the general action of aero- 
planes, but have not the time to make a real 
study of them. W. J. HUMPHREYS 
A Manual of Philippine Silk Culture. By 
Cuartes S. Banks, Department of the In- 
terior, Bureau of Science, Manila, 1911. 
Mr. Banks has been engaged, among his 
other duties, in a study of the possibilities in 
the way of profitable silk culture in the Philip- 
pines ever since the Bureau of Science was 
started, and this manual puts into convenient 
shape the results of his investigations. It is 
a royal octavo pamphlet of about fifty pages, 
with 18 good halftone plates and diagrams of 
rearing house and reel. He gives directions 
for the care of the domestic mulberry silk- 
worm, and announces a cross between the Ben- 
SCIENCE 
in pressure must - 
[N. S. Vou. XXXV. No. 894 
gal-Ceylon and Japanese silkworms which he 
terms “the Philippine race of silkworms.” 
He also announces the successful introduction 
of the Eri or Castor silkworm (Attacus ricint 
Boisd.) from Ceylon. He thinks that the silk 
produced from this insect will be popular not 
only among the Christian Filipinos, but also 
among the mountain tribes and the Moros, 
and further that it will find a sale among the 
Americans and Europeans for hangings, up- 
holstery and even for heavy dress goods. He 
concludes that, with both the mulberry and 
the Eri silkworms, the industry can be carried 
on in the Philippines under conditions as 
favorable as those which obtain in the best 
silk-producing countries in the world, with 
the added advantage that no disease has ap- 
peared as yet. That every effort is being made 
to prevent the introduction of disease is 
shown by the act of August 14, 1907, prohibit- 
ing the importation of silkworms, either eggs 
or cocoons, into the Philippine Islands except 
by the Bureau of Science. 
L. O. H. 
SPECIAL ARTICLES 
FOSSIL HOLOTHURIANS 
Frw classes of animals have a less satis- 
factory geological record than the holothu- 
rians and every fragment that can be gathered: 
is therefore of unusual interest and import- 
anee. The known records occur in two forms, 
impressions of the whole animal or much 
more commonly, nearly or quite microscopic 
caleareous particles imbedded in fine shales 
and limestones and resembling more or less 
nearly the similar calcareous particles found 
in the body-wall of most living holothurians. 
Ludwig* has well summed up the phylogenetic 
value of these fossil particles: 
Solehe Reste aus dem Kohlenkalk, dem Jura, der 
Kreide und dem Tertiaér vorliegen, aber keine 
sichere Bestimmung nach Art, Gattung und Fam- 
ilie gestatten: nur die eocinen Synaptidenreste 
. . machen davon eine Ausnahme, da sie sich mit 
einiger Sicherheit auf die Gattungen Synapta, 
Chiridota (oder Trochodota) und Myriotrochus 
beziehen lassen. 
11892, ‘‘Die Seewalzen,’’ p. 446. 
