12 Charles Grafton Page. 
iments were, however, made to measure its power. The ex- 
Jou 
announces that the engine had subsequently reached ten horse- 
power. The inquiry will of course arise what fractional part 
this engine realized of the whole power due to the galvanic 
current of the battery used, which, if the determination of 
Petrie in 1850, may be relied on, is one horse-power for one 
and a half (1°56) pounds of zine per hour consumed in a Dan- 
iell’s battery, or about six tenths of that weight consumed in 
a Grove’s battery. This point does not appear to have been 
tested at all in the experiments made by Prof. Johnson. Some 
observations were made by Prof. Page himself and his chief 
engineer, of the consumption of zinc to the horse power in one 
of the engines tried, but it was our impression at the time 
that they were not carried far enough to give reliable results. 
In fact Prof. Page thought these tests of less importance than 
attention to the working of some of the details of the engine, 
and in an important sense he was right in this, since the theo- 
retical mechanical equivalent of zinc consumed is best found 
without an engine, and the elementary conditions of high eco- 
nomic efficiency in the action of the galvanic current in these 
“axial engines” are easily recognized. One of these is to 
avoid the waste of power in heavy induction sparks, and to 
the subject of these induction sparks he gave a great deal of 
attention, though, till after the close of his experiments, he did 
not hit upon a method of getting rid of the particularly heavy 
induction spark at the end of the stroke. Subsequently, how- 
ever, he devised and described in the American Polytechnic 
Journal, vol. i, p. 369, a device by which this may be effected. 
By this device no coil cirewit need be broken with a current 
in it, and we do not think, as he seems to, that its use need be 
restricted to a slow motion of the engine. We also believe 
that he modestly overrates the objection to the momentary 
closing of the battery, incident to this device, in a short cir- 
cuit or by a resistance wire, and the spark from the immediate 
breaking of the battery circuit so formed. Ifa resistance wire 
