which should be discharged; and that whatever is conducive to its preservation, may not be uselessly wasted. If the evacuations be disordered, the most rigid adherence to dietetic rules will not contribute to the continuance, or restoration of health; these rules, however, may often be dispensed with, provided the evacuations be regular.
It is not only the noxious, or corrupt matter, which is removed by this process, but also the useful fluids, if they abound, such as the milk, blood, &c. to which subjects we refer, and likewise to the articles Ear, Nose, Urine, &c.
EVAPORATION, is the conversion of fluids, chiefly of water, into vapour which is specifically lighter than the atmosphere.
There is no subject that has occasioned a greater variety of opinions than the theory of evaporation; but, consistently with our plan, we shall recite only a few established facts.
Evaporation is one of the great chemical processes by means of which Nature supplies the whole vegetable kingdom with the dew and rain necessary for its support. Hence, it takes place at all times, not only from the surface of the ocean, but also from that of the earth. Nor is it confined to these: it is even carried on from the leaves of trees, grass, &c. with which the earth is covered. Great part of the water which is thus raised, descends again during the night, in the form of dew, being absorbed by those vegetables which yielded it before.
One of the most beneficial effects of evaporation is, to cool the earth, and prevent it from being too much heated by the sun. This property of producing cold, by evaporation, has but lately been observed by chemists, who have accordingly availed themselves of it in its fullest extent; though their mode of procuring cold, by means of those expensive fluids, ether and spirit of wine, can only be employed by way of experiment. The most simple method, however, of producing cold by the evaporation of water, may be applied to various useful purposes, especially in warm countries: thus sailors are accustomed to cool their casks of liquors, by sprinkling them with sea-water.—See also Ice.
Dr. Darwin justly observes, that the evaporation of moisture from the surface of the earth, produces so much cold as to injure those terrestrial plants which are too long covered with it. Hence such parts of wall-trees as are sheltered from the descending dews, by a coping stone on the wall, are not so liable to be injured by frosty nights; because they are not made colder by the evaporation of the dew, and also have less water to be congealed in their vessels, and to burst them by its consequent expansion.
EVENING, is that part of the night which commences with sunset, and properly terminates when the prudent and industrious repair to their couch—long before midnight.
In countries surrounded by the ocean, the evenings are generally damp and chilly, so that the temperature of the air is many degrees colder than in the preceding day. Hence the necessity of adopting a warmer dress than usually worn, if we are obliged to expose ourselves to the evening-air: invalids and convalescents ought not to leave their apartments after sun-
