e
dynamite guns, as demonstrated in the Cuban campaign, is a step in this
direction. And, indeed, the use of compressed air in many commercial
fields already competing with steam and electricity is a step towards
the use of air still further compressed, and cooled, meantime, to a
condition of liquidity. The enormous advantages of the air actually
liquefied, and so for the moment quiescent, over the air merely
compressed, and hence requiring a powerful retort to hold it, are patent
at a glance. But, on the other hand, the difficulty of keeping it liquid
is a disadvantage that is equally patent. How the balance will be struck
between these contending advantages and disadvantages it remains for
the practical engineering inventors of the future--the near future,
probably--to demonstrate.

Meantime there is another line of application of the ideas which the
low-temperature work has brought into prominence which has a peculiar
interest in the present connection because of its singularly Rumfordian
cast, so to speak, I mean the idea of the insulation of cooled or heated
objects in the ordinary affairs of life, as, for example, in cooking.
The subject was a veritable hobby with the founder of the Royal
Institution all his life. He studied the heat-transmitting and
heat-reflecting properties of various substances, including such
directly practical applications as rough surfaces _versus_ smooth
surfaces for stoves, the best color for clothing in summer and in
winter, and the like. He promulgated his ideas far and wide, and
demonstrated all over Europe the extreme wastefulness of current methods
of using fuel. To a certain extent his ideas were adopted everywhere,
yet on the whole the public proved singularly apathetic; and, especially
in America, an astounding wastefulness in the use of fuel is the general
custom now as it was a century ago. A French cook will prepare an
entire dinner with a splinter of wood, a handful of charcoal, and a
half-shovelful of coke, while the same fuel would barely suffice to
kindle the fire in an American cook-stove. Even more wonderful is the
German stove, with its great bulk of brick and mortar and its glazed
tile surface, in which, by keeping the heat in the room instead of
sending it up the chimney, a few bits of compressed coal do the work of
a hodful.

It is one merit of the low-temperature work, I repeat, to have called
attention to the possibilities of heat insulation in application to "the