THE INFLUENCES OF THE SUNBEAM ON ORGANISATION.

THE sun pours over the earth a flood of light, and under its influence we find nature assuming her myriad forms of organisation, rich in the varied beauty of colour, and wonderful in the mysterious phenomena of life. From the Sacred Volume we learn that the earth remained a chaos so long as "darkness was upon the face of the deep,” and that immediately upon the appearance of light the world became covered with organisation and life.

Although from the earliest periods of time man associated the progress of vegetable and animal life with the influences derived from the solar centre, and worshipped the visible source of light as the most exalted emblem of power to which his intelligence could rise, yet, until within a few years, he remained ignorant of the peculiar forces which are united in the silver thread of a sunbeam.

The alchemists were the first to observe a peculiar chemical change in a salt of silver when it was exposed to sunshine. They interpreted this remarkable discovery falsely, led away from the truth by their delusive dream of transmutation; and it remained a barren fact, until Scheele, a Swedish chemist, drew attention to the circumstance, that some rays, having great illuminating power, produced no change in the colour of chloride of silver, while others which were less luminous blackened that salt most readily. Since that time discoveries have been rapidly made, and we are now acquainted with at least three principles broadly distinguished from each other, namely,

LIGHT, upon which depend the phenomena of vision and the colour of bodies.

HEAT, regulating the temperature of all things.

ACTINISM, or chemical force, to which belong all the peculiarities of photographic change, and many of the chemical processes of organisation.

To an explanation of these points we must now direct attention. If through a small hole in a shutter we allow a ray of light to enter a dark room, the result is the formation of a round spot on the floor. This spot is distinguished by the eye as white LIGHT; if we place a thermometer in the luminous circle, the rise of the mercury proves that HEAT is associated with it; and if a piece of paper, covered with chloride of silver, is fixed in the path of the ray, it blackens rapidly by decomposition, showing that a force exists capable of breaking up powerful chemical combinations.

We have the means of separating, to a certain extent, these principles or powers from each other.

If in the path of the ray A B we interpose a flint-glass prism P, the ray is bent out of its path, or refracted, and

instead of having one colourless spot of light upon the floor, we have a series of coloured spots above it, overlapping each other, which is called a prismatic spectrum.