May 23, 1884.] 
The system is made still more effective by taking this 
air, not from the exhaust-pipe, but from the air-brake 
cylinders beneath the cars, and thus operating the 
continuous brakes on each car as well as the same 
work is done by the common Westinghouse system. 
The experimental engine has drawn trains of three 
and four loaded cars from Harlem to the Battery, 
New-York City, a distance of nine miles, in two 
minutes and a half less than schedule time, — forty 
minutes, — making all stops, and on three-fourths of 
a single charge of air. The engine will handle well, 
alone, with a pressure of twenty-five pounds. 
It is impracticable to cover long distances without 
refilling the reservoirs, and it is not proposed to 
attempt doing so. The reservoirs are to be filled at 
every ten-miles run, or every forty or fifty minutes; 
and filling-stations are to be provided at proper inter- 
vals along the line of the road. The reservoirs are 
so well made, that the engine stands all night, under 
a pressure of one hundred pounds, without appreci- 
able loss of pressure. 
The obvious and unquestionable advantages of this 
method of transportation are: safety from the dan- 
gers of explosion, which, aside from simple pressure, 
are unavoidable with steam and water; perfect clean- 
liness, not only on the engine, but along the line and 
on the train, in consequence of the avoidance of 
dust and smoke, and sparks from the engine; free- 
dom from gas from the locomotive; less noise than 
with the steam-engine; freedom from the annoyances 
from dripping hot water, soiling the clothing, and 
half scalding the unfortunate pedestrian beneath; 
permanence of the reservoirs, which cannot be burned 
out, as can the steam-boiler, and which cannot be 
injured by the corrosion, due to leakage of water and 
steam, which is so sefious a cause of injury to the 
steam-boiler. The engineer appreciates the latter 
points particularly, as well as the comfort of having 
no fire or fireman to look after and to distract his 
attention from his duties at the throttle, and ahead of 
the train. He is even saved the responsibility and 
taxation of ‘looking out for the water’ in the boiler, 
which is no small matter on the steam-locomotive. 
Comparing the commercial sides for the two motors, 
the air-locomotive will undoubtedly be found to cost 
much less for repairs, to lose vastly less time in the 
shops, and to demand very much less of the time of 
the engineer and of the master mechanic, when off 
the road. Whether the cost of running will be so 
small as to permit the adoption of the system on our 
elevated railroads, and other railroads to which it 
may be as well adapted, cannot, as a matter of course, 
be certainly known until the experiment shall have 
been tried under all the best conditions for its oper- 
ation. This is, in fact, the question to be deter- 
mined. The experiment on the New-York lines is 
evidently very encouraging; and it is to be hoped 
that the very favorable estimates offered by its pro- 
- moters may be confirmed by long trial, and the 
successful introduction of the motor. So far as we 
are aware, the compressed-air locomotive has hitherto 
been used only where, as in the longer lines of tun- 
nels, there existed peculiar reasons for its introduc- 
SCIENCE. 
631 
tion. The experiment is a perfectly legitimate one, 
and the new company are entitled to every favor that 
can be properly accorded those who attempt in any 
way the amelioration of the annoyances and the 
dangers of railway travel. R. H. THURSTON. 
DANTEEL’S PRINCIPLES OF PHYSICS. 
A text-book of the principles of physics. By A. 
DANIELL. London, Macmillan, 1884. 20+ 
Giaap. O°: 
Many of those who have been engaged in 
teaching physics to undergraduates during the 
last ten years have felt the want of a text-book 
more in accord with the present condition of 
the science than the majority of those accessible 
to the English-reading student. It is doubtless 
a fact, and a curious one, that those most gen- 
erally in use in this country are, or perhaps it 
is better to say were, originally translations 
from the French ; and this in spite of the gen- 
erally admitted leadership of English-speaking 
people in this department of science. 
Although, perhaps, the best attainable up to 
the present time, these English translations of 
French text-books have certainly fallen short 
of perfect adaptability to the work, and more 
and more so as the years passed by. It is true 
that an attempt has been made by the editors 
and publishers to keep pace with the rapid 
erowth of the science, but this attempt has 
met with but doubtful success. 
Any system or design or scheme which may 
have existed in some of these books in the be- 
ginning has been pretty effectually destroyed 
by the numerous additions which have been 
made from time to time, in the placing of many 
of which the convenience of the printer seems 
to have been oftener consulted than any thing 
else. 
Although one may find a brief account of 
the very latest discovery or invention up to the 
time of going to press, he is likely to find it in 
a most unexpected place; and, although here 
and there will be found detailed fragments of 
modern theory, they are often so purely frag- 
mentary as to be quite unintelligible to the 
student. In fact, the book comes to resemble 
a conglomerate in its structure; and the stu- 
dent, in attempting to ‘go through it,’ meets 
with sudden and remarkable changes in hard- 
ness and density. The fact is, the change 
which has been going on in the science of 
physics during the last fifteen or twenty years 
does not consist alone in the series of brilliant 
discoveries and inventions which have brought 
it glory and renown: along with these there 
