TRANSACTIONS OF THE SECTIONS. 25 
the fact that, if the current exist, 2 will arise the same as before, whether there be 
chemical action or not, as, for example, when the current has a thermal origin; 
and that it is not derived from the heat evolved is evident also from the fact that 
it has no existence when the heat is present in the circuit without the current. 
The mechanical work is therefore, contrary to the above theory, derived directly 
from the electric current; and it follows from hence that when we have two cur- 
rents equal in every respect, the one performing mechanical work and the other 
roducing nothing bot heat, less heat must be evolved by the former current than 
y the latter; consequently the law involved in the theory, viz. that the heat evolved 
in similar conductors is proportional to the square of the currents, does not hold 
true when one of the currents produces magnetical effects. 
Facts seem to lead to the following theory asa true explanation of the mechanical 
power of electro-magnetism. Whatever our views may be regarding the nature of 
the electric current, we must allow that the molecules of bodies offer a certain 
amount of resistance to the passage of the current, which amount differs according 
to the nature of the body through which the electricity is propagated. It must also 
be admitted that the molecules of the body, in consequence of the resistance which 
they offer, become heated. Let us take now the case of the conducting wire con- 
necting the pole of a battery. Suppose it to be composed of a succession of mole- 
cules A, B, C, D, &c. The chemical action in the battery communicates a certain 
amount of motion to the atom A, in consequence of which its equilibrium is de- 
stroyed, and to regain this state it transmits motion to the next adjoining atom B; 
but B offers resistance to A, and the consequence is that A is unable to communi- 
cate to it the full amount of motion necessary to restore its own equilibrium, so 
that A must still retain a portion of the disturbing force or motion received from 
the battery; but on account of its position in space being limited by its relations 
to surrounding molecules, it can only retain motion or force in itself by vibrating, 
and in virtue of these vibrations we affirm it to be hot. Bin like manner, to regain its 
equilibrium, transmits motion to C, but C likewise offers resistance to B, and, of 
course, B must also retain a portion of the disturbing force in the form of heat, and 
what holds true of A, B, and C, holds equally true in regard to all the other mole- 
cules of the conductor. 
Let us now observe what takes place when work is being performed by an elec- 
tro-magnetic engine. We have, in the first place, a continual evolution of force 
arising from chemical action in the battery. This chemical force becomes imme- 
diately transformed into electric current, and the electric force must in turn be 
constantly transformed into some other form of force, or else we should instantly 
have an accumulation of current. When the current is allowed simply to circulate 
in the conductor without producing any work, either chemical or magnetical, its 
entire force is transformed into heat, and the heat in turn is transmitted to sur- 
rounding objects and radiated into space. This, as we have shown, is the effect of 
forces tending to a state of equilibrium. When the soft iron of the electro-mag- 
netic engine is brought into the presence of the conductor, another channel or out- 
let is then offered to the molecules of the conductor, whereby they may get rid of 
the disturbing force, the electric current; a portion of this force will be transferred 
to the molecules of the iron, causing them to assume the magnetic state, and, of 
course, whatever is consumed in work upon the molecules of the iron cannot appear 
in the molecules of the conductor in the shape of heat. The moment the mole- 
cules of the iron assume the magnetic state, no further transference of force in this 
direction can take place; but if they are allowed to perform mechanical work while 
they are assuming this state, as is the case when the electro-magnetic engine is in 
motion, then a constant outlet is afforded in this direction to the disturbed mole- 
cules of the conductor to regain their equilibrium. But it must be observed that 
the relative proportions of the force which pass through each of the two channels 
or outlets, heat and magnetical work, do not remain the same, as Dr. Joule and 
Dr. Scoresby’s theory implies; for as the force will always tend to the path of least 
resistance, the relative proportion passing through each outlet will be determined 
by the relative resistance offered—the quantity passing through each being in- 
versely as the resistance to be overcome. Now the quantity « of mechanical work 
that can be produced by an electro-magnetic engine from a given quantity of elec- 
