WeBRuUARY 16, 1912] 
can be understood by the average boy, and yet 
it explains many facts that often are either 
wholly ignored or, for the average reader, told 
only in unintelligible symbols and signs. 
For the non-mathematical reader, and for 
the man who does not care for a large volume 
on the subject, this probably is one of the best 
books available. 
The Aeroplane. By T. O’B. Hussarp, J. H. 
Leprporr and ©. C. Turner. Longmans, 
Green and Oo., X.; 127, price 2 shillings 6 
pence. 
There is an old proverb to the effect that 
“too many cooks spoil the broth,” and it 
seems to be eminently applicable in the pres- 
ent case. ‘ 
The first chapter deals with the properties 
of the air, and is so full of errors that it 
would take another chapter to correct them. 
A simple example will sufiice: 
Now the density of water-vapor is 0.625 of that 
of air, and since air can contain a portion of 
water-vapor amounting to 3 per cent. of its vol- 
ume, it is obvious that saturated air is lighter than 
dry air. 
This statement would be pretty hard to 
beat in a contest for number of errors in a 
single sentence. One had as well say that 
since a sponge can contain water that there- 
fore a saturated sponge is lighter than a dry 
one. 
As a matter of fact moist air is lighter than 
dry air at the same temperature and pressure, 
but the authors have not explained the cor- 
rect reason. 
The rest of the book, after the first chapter, 
is fairly good for the popular reader and has 
the excellent feature of conspicuous division 
into topics, but it is marred here and there by 
the presentation of rough approximations in 
the guise of exact values. 
Bird Flight as the Basis of Aviation. By 
Orro LitientHat. Longmans, Green and 
Co., XXIV., 149. 
This of course is a translation of an old 
-and well-known German book. But the trans- 
lation was worth while, since it enables a 
larger number of persons to read for them- 
selves Lilienthal’s accounts of numerous ex- 
SCIENCE 
273 
periments based upon careful studies of birds 
and their mode of flight. It is astonishing 
how many experiments he and his brother 
made, and what generally well-founded con- 
clusions they reached. Otto Lilienthal was 
one of the enthusiastic pioneers in the experi- 
mental study of aviation and his work un- 
doubtedly contributed materially to the final 
accomplishment of mechanical flight, albeit 
along lines different from those he believed 
the most practicable. He believed that na- 
ture’s method is always the best method—for- 
getting, possibly, that the locomotive, though 
swifter than the greyhound, runs on wheels 
and not on legs—and so he strove to fly, as do 
the birds, with beating wings and soaring. 
Soaring, at least, is greatly to be desired, 
and likely some day to be fully achieved, and 
so this book, by one of the most enthusiastic 
advocates of bird flight, still has a freshness 
about it and much of interest; in fact it is 
one of the few aviation classics. 
By G. C. Lornine. 
New York, XIV., 331, 
Monoplanes and Biplanes. 
Munn and Co., 
price $2.50. 
This book is not adapted to the taste of the 
general reader—it is neither poetry nor ro- 
mance—but to the man who is seriously study- 
ing aeronautics and needs to know how the 
various types of aeroplanes are made it is well 
nigh invaluable. 
It begins with a short but appreciative ac- 
count of the work of Langley, Lilienthal and 
Chanute. This is followed by several excel- 
lent chapters on air resistances and air fric- 
tion, with numerical examples applicable to 
aeroplane designing. 
After this, various types of aeroplanes, 18 
monoplanes and 20 biplanes, are described in 
detail and intercompared. A separate chapter 
is devoted to the different types of controlling 
apparatus, and another timely and sensible 
chapter, to accidents and their various causes. 
Every chapter is profusely illustrated, and 
in the great majority of cases the illustrations 
are extremely helpful to the reader. There 
also are numerous references to original 
articles which may be consulted by those who 
wish more detailed information. 
