38 
for the theories and examples are presented 
with little comment and the writer is “ satis- 
fied to let the reader draw his own conclu- 
sions.” With what Hancock gives, the reader 
would doubtless conclude that everything was 
readily explained by the theories presented— 
though by this method the theories have the 
advantage of being clearly and definitely 
formulated. The reader is rather disap- 
pointed when he finds that the hundred-page 
chapter headed “ Ecology—Interpretation of 
Environment as Exemplified in the Orthop- 
tera” consists mostly of short descriptions of 
the habits of grasshoppers, and he looks in 
vain for the “ interpretation.” 
The general reader will probably be con- 
fused where such terms as lores, calamus, 
rachis, vanes, barbs, barbules (p. 46) and luna 
(p. 60) are introduced without explanation. 
There is frequent and somewhat monotonous 
allusion to a “plate photographic illustra- 
tion” which is often several pages from the 
reference. The reader would have been saved 
much time by a page reference. At the top of 
page 384 reference is made to a plate that ap- 
peared in the American Naturalist in 1905 
but does not appear in the book! Among 
other loose and careless statements, such as 
are likely to appear in any first edition, the 
following may be mentioned: Humming birds 
are said to occur “in the tropics” and they 
are found only in America (p. 43). On pages 
73 and 75 “this species” is discussed when 
no species has been mentioned; on page 86 
the pronoun “them” refers to “substance.” 
The following sentence occurs on page 299: 
“The cherries were luciously ripe, and after 
eating a few, one is apt to feel a dislike for 
their pungent flavor.” “Geophilous” is 
used to designate animals that feed on the 
surface of the ground (p. 356), and one 
wonders how an animal like the earthworm, 
that eats dirt, would be classified. These defi- 
nitions are given (pp. 482 and 433): “ Desert: 
Vast sandy tracts of land, appearing in west- 
ern United States, where evaporation exceeds 
rainfall. . . . Man’s Houses: Country and 
City Houses; (a) basement; (b) upper floor.” 
SCIENCE 
[N.S. Vou. XXXV. No. 888 
Rana catesbiana appears on page 300 as R. 
catisbiana and on the plate facing this page 
as R. catisbiant. It is difficult to understand 
the writer’s meaning when (p. 356), after 
stating that short-winged acridians are less 
numerous in treeless, arid districts than in 
humid, forested regions and that most flight- 
less species of locusts are plant-feeding as 
distinguished from ground-feeding, he says: 
“My own conclusions . . . is simply this: 
that it is a question of food supply and nutri- 
tion derived therefrom. In the case of short- 
winged forms, they are due to under-develop- 
ment as the result of scant food.” 
A. S. PEARSE 
SPECIAL ARTICLES 
ON POWERS OF TEN 
For expressing numerically the widely 
varying magnitudes occurring in scientific 
work, two methods are in common use. Both 
are adequate and accurate, but results ex- 
pressed by means of one are much more easily 
grasped and remembered than with the other. 
The more convenient method appears to be 
gaining in use. The present paper is written 
with the idea that this desirable change may 
be accelerated if the advantages of the method 
are stated, and thus presented to those who 
have hitherto not given the matter special 
attention. 
The simplest way of writing a number is, 
of course, to write it out in Arabic notation. 
But this, in general, involves the presence of 
numerous ciphers, which the reader must 
count in order to learn what the number is. 
There is, therefore, a gain if the writer counts 
the ciphers for him and records the number 
obtained. Hence the familiar system, where 
a number is given as the product of (1) a 
series of significant digits, and (2) ten, with 
an exponent (e. g., the velocity of light is 
3X 10” em. per sec.). 
This system has still one great disadvan- 
tage: it calls in each case for the reading of 
two numbers, and thus greatly increases the 
strain on both the attention and the memory. 
And this difficulty is multiplied when the 
