results therefrom. It will, I hope,
be seen that, with all the safeguards we have provided, we may fairly
reckon upon having for sale the stated quantity of air produced by means
of the plant, as estimated, and at the specified annual cost; and that
therefore the statement of cost per indicated horse power per annum may
be fairly relied upon. Thus the cost of compressed air to the consumer,
based upon an _average_ charge of 5d. per 1,000 cubic feet, will vary
from L6 14s. per indicated horse power per annum to L18 13s. 3d.,
according to circumstances and mode of application.

A compressed air motor is an exceedingly simple machine--much simpler
than an ordinary steam engine. But the air may also be used in an
ordinary steam engine; and in this case it can be much simplified in
many details. Very little packing is needed, as there is no nuisance
from gland leakage; the friction is therefore very slight. Pistons and
glands are packed with soapstone, or other self-lubricating packing; and
no oil is required except for bearings, etc. The company will undertake
the periodical inspection and overhauling of engines supplied with their
power, all which is included in the estimates. The total cost to
consumers, with air at an average of 5d. per 1,000 cubic feet, may
therefore be fairly taken as follows:

Min. Max.
Cost of air used L6 14 01/2 L18 13 3
Oil. waste, packing, etc. 1 0 0 1 0 0
Interest, depreciation,
etc., 121/2 per cent. on
L10, the cost of engine
per indicated
horse power 1 5 0 1 5 0
-------- ---------
L8 19 01/2 L20 18 3

The maximum case would apply only to direct acting engines, such as
Tangye pumps, air power hammers, etc., where the air is full on till the
end of the stroke, and where there is no expansion. The minimum given is
at the average rate of 5d. per 1,000 cubic feet; but as there will be
rates below this, according to a sliding scale, we may fairly take it
that the lowest charge will fall considerably below L6 per indicated
horse power per annum.--_Journal of Gas Lighting_.

* * * * *

THE BERTHON COLLAPSIBLE CANOE.

An endeavor has often been made to construct a canoe that a person can
easily carry overland and put into the water without aid, and c