Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/48

30&#93; jo] COL it is the most beneficial temperature in the care of febrile, and such dis- eases as are not attended with ex- treme debility ; but it should never be followed by any considerable degree of heat. Sydenham, more than a century ago, pointed out the evils attendant on too much heat in sick-rooms ; he seldom would allow his patients even to lie in bed, and very judiciously directed the rooms to be constantly venti- lated with cool air. The great be- nefit derived from this practice in the small-pox, is now generally ac- knowledged, and arises chiefly from avoiding the stimulus of heat, after its operation. The great cold produced by evaporation, observes Dr. Dar- win, is now well understood. In all chemical processes, where aerial or fluid bodies become consoli- dated, part of* the. latent heat is pressed out, as in the instant when water freezes, or unites with quick- lime. On the contrary, when solid bodies become fluid, or fluid ones become aerial, heat is absorbed bv the solution : whence it may be said, in general, that all chemical combinations produce heat, and all chemical solutions generate cold. This should teach the careful gar- dener, nht to water tender vege- tables in the heat of sun-shine, or in a warm dry wind, lest the hasty evaporation should. produce so much cold as to destroy them; an effect that will the more cer- tainly follow, as they have been previously too much stimulated by heat, in consequence of which, the power of life, or irritability, had been already diminished. When treating on the diseases of plants, Dr. Darwin remarks, that though excessive heat is sel- dom very injurious to vegetation in COL this country, yet the defect of thai element, or in common language, excess of cold, is frequently de- structive to the tender shoots of the ash, and the early blossoms of many fruit-trees, such as apples, pears, apricots, &c. — The I lights occasioned by frost, generally hap- pen in the spring, when warm sunny days are succeeded by cold nights, as the living power of the plant has then been previously ex- hausted by the stimulus of heat, and is therefore less capable of being ex- cited into the actions necessary to vegetable life, by the greatly dimi- nished stimulus of a freezing at- mosphere. In the northern climates of Swe- den and Russia, where long sunny days succeed the melting of copi- ous snows, the gardeners 'are obliged to shelter their wall-trees from the meridian sun, in the ver- nal months ; an useful precaution, which preserves them from the violent effects of cold in the suc- ceeding night ; and, by preventing them from flowering too early, avoids the danger of the vernal frosts. In a similar manner, the destruction of the more succulent parts of vegetables, such as their early shoots, especially when ex- posed to frosty nights, can only be counteracted by covering them from the descending dews, i rime, by the coping stones of a wall, or mats of straw. Having given a short account of the sensible effect of a cold tem- perature on animal and vegetable life, we shall conclude with a few remarks connected with the natu- ral history of this elementary power. — The properties of cold seem to be directly opposite to those of heat : the latter increases the bulk of all bodies j the for- mer