8 
development of power, of whatever kind, is always accompanied 
by a change in the form of matter somewhere. To obtain a 
oiven amount of exertion from a horse we learn that it is 
Ct 
necessary to give him a larger quantity of food than when he 
is at rest. If we desire to impel a locomotive engine at a high 
velocity we are compelled to supply an increased quantity of 
fuel, that steam may be generated with greater rapidity. We 
know of no development of force, whether heat, light, electricity, 
or muscular power, without such a change in the form of matter 
as amounts, to us, to its destruction. Muscle is consumed in 
every exertion of animal strength. Carbon and hydrogen in 
like manner are burnt in producing our artificial lights, cither 
as gas, oil, wax, or tallow, and also in the production of heat, 
whether in our domestic fires, the furnaces of our manufactories, 
or the boilers of our steam engines. We evoke electricity by 
several methods of disturbance, but we have only now to 
consider that means of development which depends upon 
chemical action. Although avc employ magnetic force, this is 
dependent on the power which is produced in the voltaic 
battery, and the zinc or any other element which may be 
employed is converted into some new form. Zinc, for example, 
is changed by the action of sulphuric acid in the battery into 
sulphate of zinc ; and the advocates of the application of elec- 
tricity as an illuminating or moving agent on the ground of 
-economy state, and truly state, that the salt may be reduced 
and the metal revived. From my investigations of the Avhole 
question I feel assured that I state a truth in saying the coal 
employed in reproducing the metal would afford as much 
light, heat, or mechanical power as that obtained by the 
destruction of the metal in the first instance in the battery. 
Let me not be misunderstood. In the present state of our 
knowledge I deem it hazardous to attempt to apply electro- 
magnetism instead of steam. Notwithstanding the rapid 
discoveries made in every branch of electrical research, and the 
great power Avhich we can command in our voltaic arrangements, 
it must not be forgotten that the quantity of electricity obtained 
is exceedingly small in comparison with the quantity which exists 
in the elements constituting the voltaic battery. Dr. Faraday, 
