Page:Popular Science Monthly Volume 60.djvu/268

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of years the moon will be a full moon in the sky, but a new moon in the calendar. Nothing could be neater than the presentation of this dilemma.

Bacon understood the theory of vision, the anatomy of the eye and much of the physiology of perception, as well as the theory of lenses and of the simple microscope. He did not combine two lenses to make a telescope, but he was on the high road to it. His works on alchemy were undertaken in the same scientific spirit, though in the infancy of chemistry they led to few results of value. Gunpowder he knew, very likely through the Arabs or the Greeks of Constantinople, who had it from the east. The children of his time played with it, he says.

No better example of the experimental method imagined and extolled by Bacon can be given than an analysis of his brilliant demonstration of the nature of the rainbow. Let the experimenter, he says, first consider the cases in which he finds the same colors; as in the hexagonal prisms of Iceland spar, for example. By looking into these he will see the rainbow hues. Many think that these arise from some special virtue of the stones, or from their hexagonal figure. Let the experimenter therefore go on and he shall find the same colors in other stones of other shapes, as well as in the drops of water dashed from oars in the sunshine, and the like. All these are instances like the phenomenon of rainbow colors. With regard to the form of the bow he is still more precise. He bids us measure the altitude of the bow and of the sun and note that the center of the bow is exactly opposite to the sun. He explains its circular form—its independence of the form of the raincloud—its moving when we move—its flying when we follow—by its consisting of reflections from a vast multitude of minute drops of rain. In the iris shown by the spray of a waterfall we may see the whole circle. In the sky the plane of the horizon comes in to interfere. Each drop of rain in the cloud is to be regarded as a spherical mirror.

His views of the nature of force are expansions of those held vaguely by Democritus and Lucretius. A body is a center of force from which energies radiate in every direction. Every action is accompanied by a reaction, and there is an interchange of force between all bodies of the universe. The propagation of force, of light for example, requires time. "There is no substance on which the action involved in the passage of a ray may not produce a change. Thus it is that rays of heat or sound penetrate the walls of a vessel of gold or brass. In any case, there are many dense bodies which altogether interfere with the visual and other senses of man so that rays cannot pass so as to produce an effect on human sense and yet, nevertheless, rays do really pass, though without our being aware of it." These precise statements were mere words to his contemporaries and could not