Page:Popular Science Monthly Volume 1.djvu/754

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738
THE POPULAR SCIENCE MONTHLY.

There is, however, one point to which he refers which should not be overlooked. Whatever views we may be disposed to entertain respecting either the mental conditions in which these phenomena originate, or the external agencies by which these conditions are produced or modified, there is reason to believe that the appearances themselves are really formed upon the retina of the eye, and thus they may be fairly placed in the category of "things actually seen."—Science Gossip.

 
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COAL AS A RESERVOIR OF POWER.
By ROBERT HUNT, F. R. S.

THE sun, according to the philosophy of the day, is the great store-house of Force. All the grand natural phenomena are directly dependent upon the influence of energies which are poured forth without intermission from the central star of our system. Under the influences of light, heat, actinism, and electricity, plants and animals are produced, live, and grow, in all their infinite variety. Those physical powers, or, as they were formerly called, those imponderable elements, have their origin in one or other of those mysterious zones which envelop the orb of day, and become evident to us only when mighty cyclones break them up into dark spots. Is it possible to account for the enormous amount of energy which is constantly being developed in the sun? This question may be answered by saying that chemical changes of the most intense activity are discovered to be forever progressing, and that to these changes we owe the development of all the physical powers with which we are acquainted. In our laboratory we establish, by mechanical disturbance, some chemical phenomenon, which becomes evident to our senses by the heat and light which are developed, and we find associated with them the principle which can set up chemical change and promote electrical manifestations. We have produced combustion, say, of a metal, or of a metallic compound, and we have a flame of a color which belongs especially to the substance which is being consumed. We examine a ray of the light produced by that flame by passing it through a prism, and this analysis informs us that colored bands, having a fixed angle of refraction, are constant for that especial metal. Beyond this, research acquaints us with the fact that, if the ray of light is made to pass through the vapor of the substance which gives color to the flame, the lines of the spectrum which were chromatic become dark and colorless. We trap a ray of sunlight and we refract it by means of a spectroscope an instrument giving results which are already described in this journal[1] when we detect the same lines as those which

  1. Popular Science Review, vol. i., pp. 210-214.