el. The arrangement depends
upon the fact that a stream of gas ascending in a heavy liquid behaves
in the same way as a stream of water descending by its own weight and
turning a water-wheel. It supplies what is perhaps the simplest and
most inexpensive small motor available for the lightest domestic work
to which a gentle but continuous source of power is applicable.

For actually cooling the air, as well as keeping it in motion, similar
devices will be resorted to, with the addition of the circulation of
the current of air through coils of pipes laid under the surface of
the ground. In this way householders will have all the advantages of
living in cool underground rooms without incurring the discomforts and
dangers which are often inseparable from that mode of life. In the
coastal regions, which usually have the most trying climates for
Europeans living in tropical countries, a method of cooling the houses
will be based on the fact that at moderate depths in the sea the
prevailing temperature is a steady one, not much above the freezing
point of water. Almost every seaport town within the tropics--where
white residents in their houses swelter nightly in the greatest
discomfort from the heat--is in close proximity to deep ocean water,
in which, at all seasons of the year, the regular temperature is only
about thirty-four degrees Fahr. The cost of steel piping strong enough
to withstand the pressure of the water in places which possess
absolutely the coolest temperature of the ocean would be very heavy;
but, on the other hand, the actual reduction of heat demanded for the
satisfactory cooling of the air in a dwelling-room is not by any means
great, and at quite shallow depths the heat of the air can be
satisfactorily abstracted by the sea water surrounding coils of pipes.

Even in colder climates it seems likely that similar systems will be
found useful in producing a preliminary reduction in the temperature
of the air employed in keeping fresh foodstuffs such as meat, fruits
and vegetables. Fruits especially, when placed in suitable
receptacles, and stored at temperatures quite steady at about the
freezing point of water, will not only be readily kept on land from
one season to another, but will be transported to markets thousands
of miles distant from the growers, and sold in practically the same
condition as if they had just been picked from the trees. During the
twentieth century the proportion of the fruit eaters