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embrace what is called the regenerative principle—a term which has, with 
reason, been objected to, as implying a restoration of expended heat. The 
so called “‘ regenerator ” is a contrivance for arresting unutilized heat rejected 
by the engine, and causing it to operate in aid and consequent reduction of 
fuel. 
It is a common observation that before coal is exhausted some other motive 
agent will be discovered to take its place, and electricity is generally cited as 
the coming power. Electricity, like heat, may be converted into motion, and 
both theory and practice have demonstrated that its mechanical application 
does not involve so much waste of power as takes place in a steam-engine ;_ but 
whether we use heat or electricity as a motive power, we must equally depend 
upon chemical affinity as the source of supply. The act of uniting to form a 
ehemical product liberates an energy which assumes the form of heat or 
electricity, from either of which states it is convertible into mechanical effect. 
In contemplating, therefore, the application of electricity as a motive power, 
we must bear in mind that we shall still require to effect chemical combina- 
tions, and in so-doing to consume materials. But where are we to find mate- 
rials so economical for this purpose as the coal we derive from the earth and 
the oxygen we obtain from the air? The latter costs absolutely nothing; 
and every pound of coal, which in the act of combustion enters into chemical 
combination, renders more than two and a half pounds of oxygen available 
for power. We cannot look to water as a practicable source of oxygen, for 
there it exists in the combined state, requiring expenditure of chemical 
energy for its separation from hydrogen. It is in the atmosphere alone that 
if can be found in that free state in which we require it, and there does not 
appear to me to be the remotest chance, in an economic point of view, of being 
able to dispense with the oxygen of the air as a source either of thermo- 
dynamic or electrodynamic effect. But to use this oxygen we must consume 
some oxidizable substance, and coal is the cheapest we can procure. 
- There is another source of motive power to which I am induced to refer, 
as exhibiting a further instance in which solar influence affords the means 
of obtaining mechanical effects from inanimate agents. I allude to the 
power of water descending from heights to which it has been lifted by 
the evaporative action of the sun. To illustrate the great advantage of 
eollecting water for power in elevated situations I may refer to the water- 
works of Greenock, where the collecting-reservoirs are situated at an 
elevation of 512 feet above the river Clyde. The daily yield of these 
reservoirs is said to be nearly 100,000 tons of water, which is derived from 
the rainfall on an area of 5000 acres. The power obtainable from this quantity 
and head of water is equal to that of a steam-engine of about 2000 horse- 
power, and the whole effect might be realized on the margin of the river by 
bringing down the water in a pipe of sufficient capacity, and causing it to 
act as a column on suitable machinery at the foot of the descent. But the 
hydraulic capabilities of the Greenock reservoirs sink into insignificance when 
compared with those of other localities where the naturally collected waters 
of large areas of surface descend from great elevations in rapid rivers or ver- 
tical falls. Alpine regions abound in falls which, with the aid of artificial 
works to impound the surplus water and equalize the supply, would yield 
thousands of horse-power ;. and there is at least one great river in the world 
which in a single plunge developes sufficient power to carry on all the ma- 
nufacturing operations of mankind if concentrated in its neighbourhood. 
Industrial populations have scarcely yet extended to those regions which 
afford this profusion of motive power, but we may anticipate the time 
