184 REPORT—1850. 
ant fact, that one horse power is the theoretic or absolute dynamic force possessed by a 
current of electricity derived from the consumption of 1°56 (one and fifty-six hun- 
dredths) pounds of zine per hour, in a Daniell’s battery. But the best electro-mag- 
netic engine that we can hope to see constructed, cannot be expected to give more 
than half or a fourth of this power: in any case, we see here the limit of power 
which no perfection of apparatus can make it exceed. 
The peculiar mode in which the electric current produces dynamical effects has 
led to much miscalculation respecting the power obtainable from it. In any sort of 
electric engine the material to which the neighbouring current gives motion, whether 
it be another moveable current, or what is more usual, a magnetic body, is impelled 
in one direction with a constant force ; and this force, whether it be attraction, re- 
pulsion, or deflection, is, like the power of gravity, sensibly constant at all velocities, 
however fast the body recedes before the action of the force ; provided only the same 
quantity (per minute) of electric current be maintained. This is quite different from 
the action of steam power, in which, the faster the piston moves the greater is the 
volume of steam per minute that must be supplied to move it, or else the less will be 
the power with which it moves. 
This fact, then, that the force with which an electric current, of a given ‘ quantity,’ 
moves the machine, is the same at any velocity of motion, bears no analogy to the 
case of steam, but would indicate that the dynamic result obtainable from a given 
electric current might be indefinitely great ; and so it would be, were it not that the 
part moved always tends to induce a current in the wire in the reversed direction : 
and this inducing influence, which increases with the velocity of motion, conflicts 
with the original current, and reduces its quantity, and consequently reduces the 
power of the motion, as well as the consumption of materials in the battery. Some 
have imagined that possible alterations in the position of the parts of the machine, 
or in its mode of action, would avoid the evil, or even might make the induced cur- 
rent to flow with the primary current instead of against it. The impossibility of 
this, though not readily proved in detail, can be at once proved by a reference to 
general principles ; it would, if true, be a creation of dynamic force, the evolving an 
unlimited force from a limited source. ‘The tendency to an opposing induced current 
in the primary wire must therefore be involved in the very principle of the system ; 
so that no ingenuity can ever get rid of the retarding influence of the induced action. 
And the only way to overcome its power, so as to maintain the primary current from 
falling below a given rate or quantity, when the machine is allowed to attain rapid 
motion, is to increase the electromotive power of the battery, the intensity (not the 
quantity) of the current, so that it shall be less affected by the opposing induction. 
The practical importance of these not altogether unknown truths, may justify the 
above somewhat particular notice of them. For want of a clearer apprehension of 
them, inventors have misapprehended the direction in which improvements were to 
be made, and much ingenuity and means have been wasted. 
Some of the best electro-magnetic engines of other inventors, that have been pro- 
perly tested by the author and others on a practically useful scale, have only given 
a power at the rate of fifty to sixty pounds of zinc per horse power per hour. The 
smallness of this power in comparison with the absolute value of the current (1°56 
pound zinc per horse power per hour) should not occasion surprise if we consider 
the present case of steam after many years of improvement. According to the deter- 
minations of Joule and of Rankine on heat, 1 1b. water raised 1° temperature is equi- 
valent to 700 lbs. weight raised 1 foot. ‘The author then proceeded to show that the 
best Cornish engines only yield th of the power that the combustion of the carbon 
actually represents, and many locomotives only zg5th part; showing what great 
rewards may yet await the exercise of inventive genius in this department, and that 
we need not wonder that we have as yet only obtained ;4nd part of the power pos- 
sessed by electricity. 
But it is to be remembered that there is a far greater likelihood of obtaining a , 
larger proportion of the real power from electricity than from heat, owing to the 
character of the two agents. The author then proceeded to explain the reason why 
so little of the power of heat could be obtained in a useful form even in the best 
steam-engines, and what were the difficulties for invention first to overcome in orde 
to a better result. ; 
