and compact by time; then they gradually undermine it, and promote its sinking into the sandy soil, which it does without difficulty, and altogether.  When level with the surface, they raise its walls higher; and so go on, throwing out the sand and raising the wall, till they have reached the water.  If they adopted our method, the soil is so light that it would fall on them before they could possibly raise the wall from the bottom; nor, without the wall, could they sink to any considerable depth.”  A stout square frame of wood scantling, boarded like a sentry-box, and of about the same size and shape, but without top or bottom, is used in making wells in America.  The sides of a well in sandy soil are so liable to fall in, that travellers often sink a cask or some equivalent into the water, when they are encamped for any length of time in its vicinity.

Scanty wells in hot climates should be brushed over, when not in actual use, to check their evaporation.

Snow-water.—­It is impossible for men to sustain life by eating snow or ice, instead of drinking water.  They only aggravate the raging torments of thirst, instead of assuaging them, and hasten death.  Among dogs, the Esquimaux is the only breed that can subsist on snow, as an equivalent for water.  The Arctic animals, generally, have the same power.  But, as regards mankind, some means of melting snow into water, for the purposes of drinking, is an essential condition of life in the Arctic regions.  Without the ingenious Esquimaux lamp (p. 205), which consists of a circle of moss wicks, fed by train-oil, and chiefly used for melting snow, the Esquimaux could not exist throughout the year, in the countries which they now inhabit.

That eating large quantities of snow should seriously disturb the animal system is credible enough, when we consider the very large amount of heat that must be abstracted from the stomach, in order to melt it.  A mouthful of snow at 32 degrees Fahr., that is to say, no colder than is necessary for it to be snow at all, robs as much heat from the stomach, as if the mouthful had been of water 143 degrees colder than ice-cold water, if such a fluid may, for the moment, be imagined to exist.  For the “latent heat” of water is 143 degrees Fahr.  In other words, it takes the same quantity of heat to convert a mass of snow of 32 degrees into water of 32º, as it does to raise the same mass of water from 32 degrees to 141º + 32 degrees = 175 degrees Fahr.  It takes in practice about as long to melt snow of a low temperature into water, as it does to cause that same water to boil.  Thus to raise snow of 5 degrees below zero Fahr.  To 32 degrees, takes 37 degrees of heat, and it requires 143 degrees more, or 180 degrees altogether, to melt it into water.  Also it requires 180 degrees to convert water of 32 degrees into water of 212 degrees, in other words, into boiling water.