it, it is evident that a certain number of cubic inches by measure, or the lungs full, will contain a less weight of oxygen than ever; so little, indeed, that life can barely be supported; and we need not wonder at persons lying down almost powerless in the hot and damp atmosphere, and gasping for breath. Hence we see that any method of cooling the air for Indians, instead of adding moisture, should rather take it out of the air, so as to make oxygen predominate as much as possible in the combined draught of oxygen, azote, and a certain quantity of the vapour of water, which will always be present; and hardly any plan could be more pernicious than the favourite though dreaded one by those who have watched its resultsof the wet mats. Cold airthat is, air in which the thermometer actually stands at a low readingby reason of its density, gives us oxygen, the food of the lungs, in a compressed and concentrated form; and men can accordingly do much work upon it. But air which is merely cold to the feelingsair in which the thermometer stands high, but which merely gives us one of the external sensations of coolnesson being made by a punkah, or any other mere blowing machine, to move rapidly over our skinor on being charged with watery vapour, or on being contrasted with previous excessive heatsuch air must, nevertheless, be rarefied to the full extent indicated by the mercurial thermometer, and give us, therefore, our supply of vital oxygen in a very diluted form, and of a meagre, unsupporting, and unsatisfying consistence.... The sine quâ non , therefore, for healthy and robust life in tropical countries, is air cold and drycold to the thermometer and dry to the hygrometer; or, in other words, dense, and containing little else than the necessary oxygen and azote, and this supplied to a room, fresh and fresh, in a continual current.'
He next goes on to describe the principle of his new plan of cooling:'The method by which I propose to accomplish this consummation, so devoutly to be desired, is chiefly by taking advantage of the well-known property of air to rise in temperature on compression, and to fall on expansion. If air of any temperature, high or low, be compressed with a certain force, the temperature will rise above what it was before, in a degree proportioned to the compression. If the air be allowed immediately to escape from under the pressure, it will recover its original temperature, because the fall in heat, on air expanding from a certain pressure, is equal to the rise on its being compressed to the same; but if, while the air is in its compressed state, it be robbed of its acquired heat of compression , and then be allowed to escape, it will issue at a temperature as much below the original one, as it rose above it on compression. Thus the air, being at 90 degrees, will rise, if compressed to a certain quantity, to 120 degrees; if it be kept in this compressed and confined state until all the extra 30 degrees of heat have been conveyed away by radiation and conduction, and the air be then allowed to escape, it will be found, on issuing, to be of 60 degrees of temperature. If a cooler be formed by a pipe under water, and air be forced in under a given compression at one end, and be made to pass along to the other, it may thereby, if the cooler be sufficiently extensive, be robbed of all its heat of compression; and if the apparatus is so arranged, as it easily may be, that at every stroke of the pump forcing in air at one end of the pipe, an equivalent quantity of the cooled compressed air escape from under a loaded valve at the other, there will be an intermittent stream of cooled air produced thereby, of 60 degrees Fahrenheit, in an atmosphere of 90 degrees, which may be led away in a pipe to the room desired to be cooled.'
The only difficulty to be encountered consists in the erection and working of machinery. There can be little fear on this score. We have no doubt that any London engine-maker would hit off the whole scheme of an air-cooling machine in half an hour. What is wanted is a forcing-pump wrought by a one horse or two bullock-power. This being erected and wrought outside of a dwelling, the air will be forced into a convolution of pipe passing through a tank of water, like the worm of a still, and will issue by a check-valve at every stroke of the piston into the apartments to be cooled. Properly arranged, and with a suitable supply of water trickling through the tank, air at 90 degrees will be reduced to 60 degrees or thereabouts, which is the temperature of ordinary sitting-rooms in England. What, it may be asked, will be the expense of such an apparatus for cooling the air of a dwelling-house? We are informed
that it will not be greater than that usually paid for heating with fires in this country; and if so, the expense cannot be considered a serious obstacle to the use of the apparatus. In the case of barracks for soldiers, hospitals, and other public establishments, the process will prove of such important service, that the cost, even if greater than it is likely to be, should present no obstacle to its application.