It quickens the germination of seeds; and assists in the formation of the colouring matter of leaves. Seeds and cuttings, which are required to germinate quickly, will do so under the effect of blue glass (which is equivalent to saying, the effect of an increased proportion of _actinism_), in half the time they would otherwise require. 560. _In what season of the year is the actinic power of light the greatest?_ In the _spring_, when the germination of plants demands its vitalising aid. In _summer_, when the maturing process advances, _light_ and _heat_ increase, and _actinism_ relatively declines. In the _autumn_, when the ripening period _arrives_, _light_ and _actinism_ give way to a greater ratio of _heat_. [Verse: "But as it is written, Eye hath not seen, nor ear heard, neither have entered into the heart of man, the things which God hath prepared for them that love him."--CORINTH. BOOK I., II.] We shall have frequently, in the progress of our lessons, to refer to _light_ in its connection with the chemistry of nature, and with organic life. But let us now invite the student to pause, and for a moment contemplate the wonders of a sunbeam. How great is its velocity--how vast its power--how varied its parts--yet how ethereal! First, let us contemplate it as a simple beam in which _light_ and _heat_ are associated. How deep the darkness of the night, and how that darkness clings to the recesses of the earth. But the day beams, and darkness flies before it, until every atom that meets the face of day is lit up with radiance. That which before lay buried in the shade of night is itself now a radiator of the luminous fluid. Mark the genial warmth that comes as the sister of light; then stand by the side of the experimentalist and watch the point on which he directs the shining focus, and in an instant see iron melt and stones run like water, under the fervent heat! Now look upward to the heavens, where the falling drops of rain have formed a natural prism in the rainbow, and shown that the beam of pure whiteness, refracted into various rays, glows with all the tints that adorn the garden of nature. These are the visible effects of light. But follow it into the crust of the earth, where it is, by another power, which is neither light nor heat, quickening the seed into life; watch it as the germ springs up, and the plant puts forth its tender parts, touching them from day to day with deeper dyes, until the floral picture is complete. Follow it unto the sea, where it gives prismatic tints to the _anemone_, and imparts the richest colours to the various _algae_. Think of the millions of pictures that it paints daily upon the eyes of living things. Contemplate the people of a vast city when, attracted by some floating toy in the air, a million eyes look up to watch its progress.