Marcu 29, 1912] 
their nidification presents nothing that may be 
deemed peculiar or even specially character- 
istic. In their flight and manner of procuring 
their food, however, they differ strikingly from 
all other birds, in these respects closely re- 
sembling certain insects, especially the cre- 
puscular hawkmoths (Sphingide). Their 
food, consisting mainly of small insects, but 
in part also of the nectar of flowers, is mostly 
gleaned from blossoms, before which they 
poise, with wings so rapidly vibrating as to 
be invisible except as a dim haze or halo 
partly surrounding the body and producing 
the humming sound from which these birds 
derive their vernacular name, the bill thrust 
inside the flower and the slender, semitubular 
tongue extended into the depths of the blos- 
som. Some species, instead of feeding from 
flowers, glean their insect food from the bark 
of forest trees, following along the branches 
in suspended flight in the same manner that 
the others pass from flower to flower. In their 
feeding from flower to flower, Humming Birds, 
like bees, butterflies, and moths, perform the 
same office in the economy of nature as insects 
by transferring pollen from one bloom to an- 
other, and thus assisting in the fertilization of 
plants. In flying from one point to another, 
the flight of Humming Birds, while essentially 
direct, is usually more or less undulating, and 
so extremely rapid that the eye can scarcely 
follow. Often this flight is accompanied (at 
least in the case of males of some species) by 
a more or less remarkable screeching or 
grating sound, produced mechanically by some 
peculiarity of wing-structure. 
“Diminutiveness of size and metallic bril- 
lianey of coloring are the chief external char- 
acteristics of Humming Birds, though excep- 
tions to both occur; and in these respects they, 
as a group, have no rivals. Unfortunately, 
stuffed specimens convey but a faint idea of 
their splendid coloring, for the perfection of 
their changeable refulgence can be fully real- 
ized only in the living bird, whose every 
change of position flashes to view a different 
hue—emerald green replacing ruby red, sap- 
phire blue succeeding fiery orange, or either 
becoming opaque velvety black—according to 
SCIENCE 
501 
the angle at which the sun’s rays touch the 
feathers, an effect which can only partially be 
imitated with the stuffed specimen by arti- 
ficially changing its position with reference to 
the light. Many species have a spot of the 
most luminous or brilliantly metallic color 
(usually green) that it is possible to imagine 
on the forehead at the base of the bill, this 
spot being surrounded by the most intense 
velvety black—evidently to enhance the bril- 
lianey of the ornament by contrast, just as a 
jeweler would, for the same purpose, display 
a diamond or other gem against a background 
of black velvet. Often there is a spot of bril- 
liant color and one of a contrasting hue just 
below it, the result being that first one color, 
then the other, is flashed forth as the bird 
changes slightly its position.” 
The thirty-one plates give the structural 
details of bill, wings, tail and feet of each of 
the 121 genera, thus greatly facilitating iden- 
tification. It is hoped that Part V. may be 
followed in due time by the remaining volumes 
of this invaluable work, so indispensable to all 
students of American birds. 
J. A. ALLEN 
The Hindu-Arabic Numerals. By Davw 
Evcene SmiraH and Louis CHarLes Kar- 
PInsKI. Boston and London, Ginn and 
Company. 1911. Pp. vi-++160. 
This book gives in compact form a readable 
and carefully prepared account of the nu- 
merous researches which have been made in 
the endeavor to trace the origin and develop- 
ment of the Hindu-Arabic numerals. Teach- 
ers of mathematics will welcome it, while stu- 
dents specializing in the history of mathe- 
matics will derive great help from the many 
bibliographical references to other publica- 
tions on this subject. Like the arithmetician 
Tonstall the authors read everything in every 
language and spent much time in licking 
what they found into shape ad ursi exemplum, 
as the bear does her cubs. But it would not 
be a correct statement, were we to convey the 
idea that the book does not embody original 
research. In several cases the authors have 
been able to correct mistakes of earlier writers 
