We know from experience, that the influence of light and atmospheric temperature upon living bodies is very similar, being manifested by the strongest stimulating effects; in fact, light is known to be an important agent in varying the phenomena of the atmosphere, its stimulating effects being more or less modified by light, according to the permanence and intensity of such light. The sun being the principal source of light and heat, their influences may be considered as inseparable, and acting in concert; if a thermometer were to be removed from the dark into the light, the mercury would be seen to rise, and, on the other hand, if it were to be conveyed from the light to the dark, it would fall. “In tubes of glass mercurial columns rise, Or sink obedient to the incumbent skies; Or as they touch the figured scale, repeat The nice gradations of circumfluent heat.” Milton beautifully apostrophizes the great luminary, Light, thus: “Hail, Holy Light! offering of Heaven’s first-born, Or of the eternal co-eternal beam, Bright effluence of bright essence increate,-- Thy fountain who shall tell? Before the sun-- Before the heavens thou wert, and at the voice Of God, as with a mantle, didst invest The rising world of waters dark and deep.” Commencing with the properties of light, we find its influence on inorganic bodies and vegetables to be unequivocal; in short, it may be said that so very extensive is its influence, that there is not a substance which, when exposed to its action, does not experience some alteration. Without light, independently of the heat which is its ordinary concomitant, there would scarcely exist a trace of vegetation, and when we reflect on the remarkable dependence of the animal and vegetable kingdoms on each other, the animal by the extrication of carbonic acid gas, affording a fluid essential to vegetation; the plant, on the other hand, by the emission of oxygen, supplying the atmosphere with the gas which is equally necessary for the well-being of the former, we cannot suppose light to be less essential to animal life. The chemical effects of light, and its influence on animal and vegetable vitality, have much engaged the attention of philosophers:--