utilized, and sold at a good price, then the cost of such motive power
may be reduced in proportion to the value of those by-products.

For the purpose of comparison, let us now employ the man who would
otherwise clean and prepare the primary cells, at engine driving. We let
him attend to a six horse power steam engine, boiler, and dynamo machine
for charging 50 accumulators, each of a capacity of 370 ampere hours, or
one horse power hour. The consumption of fuel will probably amount to 40
lb. per hour, which, at the rate of 18s. a ton, will give an expenditure
of nearly 4d. per hour. The energy derived from coal in the accumulator
costs, in the case of a supply of five electrical horse power for seven
hours, 2s. 9d.; the energy derived from the zinc in a primary battery,
supplying five electrical horse power for seven hours, would cost 17s.
3d.

It is hardly probable that any one would lay down a complete plant,
consisting of a steam or gas engine and dynamo, for the sole purpose of
charging the boat cells, unless such a boat were in almost daily use, or
unless several boats were to be supplied with electrical power from one
station. In order that electric launches may prove useful, it will be
desirable that charging stations should be established, and on many of
the British and Irish rivers and lakes there is abundance of motive
power, in the shape of steam or gas engines, or water-wheels.

A system of hiring accumulators ready for use may, perhaps, best satisfy
the conditions imposed in the case of pleasure launches.

It is difficult to compile comparative tables showing the relative
expenses for running steam launches, electric launches with secondary
batteries, and electric launches with primary zinc batteries; but I