Some persons judge of the wholesomeness of water through the agency of a balance:[1] their pains, however, are expended to little purpose, it being but very rarely that one water is lighter than another. There is, however, a more certain mode of ascertaining the difference in quality, that water being the better of the two which becomes hot and cold with the greatest rapidity: in addition to which, not to keep poising a balance,[2] after water has been drawn up in vessels, if it is good, it should gradually become warmer, they say, when placed upon the ground. Which water, then, of the several kinds will be most likely to be good and wholesome? Well-water, no doubt, if we are to judge from the general use made of it in cities: but only in the case of wells in which it is kept in continual agitation by repeated drawing, and is refined by the earth acting as a filter. These conditions are sufficient to ensure salubrity in water: in regard to coolness, the well must be in a shaded spot, and the water kept exposed to the air. There is, however, one thing above all to be observed, a point, too, of considerable importance with reference to the continuance of the flow—the spring must issue from the bed of the well, and not from the sides. To make water cold to the touch may be effected artificially even, either by forcing it to rise aloft or by making it fall from a height, and so come in collision with the air, and be- come incorporated[3] therewith: for in swimming,[4] we find, when we hold our breath, the water is felt to be all the colder.

It was the Emperor Nero's invention[5] to boil water, and then enclose it in glass vessels and cool it in snow; a method which ensures all the enjoyment of a cold beverage, without any of the inconveniences resulting from the use of snow. Indeed, it is generally admitted that all water is more[6] wholesome when it has been boiled; as also, that water when it has once been heated, will become more intensely[7] cold than before—a most ingenious discovery.[8] The best corrective of unwholesome water is to boil it down to one half. Cold water, taken internally, arrests hæmorrhage. By keeping cold water in his mouth, a person may render himself proof against the intense heat of the bath. Many a person knows by his own every-day experience, that water which is the coldest to drink is not of necessity the coldest to the touch, this delightful property being subject to considerable fluctuations.[9]