supply of cheap fuel to the electric
current derived at small expense from natural sources of power.

Calcium carbide, by means of which acetylene gas is obtained as a
product from water, becomes in this view stored power. The
marvellously cheap "water-gas" which is made through a jet of steam
impinging upon incandescent carbons or upon other suitable glowing hot
materials will, no doubt, for a long time command the market after the
date at which coal-gas for the generation of power has been partially
superseded.

But it seems exceedingly probable that a compromise will ultimately be
effected between the methods adopted for making water-gas and calcium
carbide respectively, the electric current being employed to keep the
carbons incandescent. When power is to be sold in concrete form it
will be made up as calcium carbide, so that it can be conveyed to any
place where it is required without the assistance of either pipes or
wires. But when the laying of the latter is practicable--as it will be
in the majority of instances--the gas for an engine will be obtainable
without the need for forcing lime to combine with carbon as in calcium
carbide.

Petroleum oil is estimated to supply power at just one-third the price
of acetylene gas made with calcium carbide at a price of L20 per ton.
This calculation was drawn up before the occurrence of the material
rise in the price of "petrol" in the last year of the nineteenth
century; while, concurrently, the price of calcium carbide was
falling. A similar process will, on the average, be maintained
throughout each decade; and, as larger plants, with cheaper natural
sources of energy, are brought into requisition, the costs of power,
as obtained from oil and from acetylene gas, will more and more
closely approximate, until, in course of time, they will be about
equal; after which, no doubt, the relative positions will be reversed,
although not perhaps in the same ratio. Time is all on the side of the
agent which depends for its cheapness of production on the utilisation
of any natural source of power which is free of all cost save
interest, wear and tear, and supervision.

Even the steam-engine itself is not exempt from the operation of the
general law placing the growing advantage on the side of power that is
obtainable gratis. One cubic inch of water converted into steam and at
boiling point will raise a ton weight to the height of one foot; and
the quantity of coal of good qual