Page:Popular Science Monthly Volume 20.djvu/808

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end of the plateau, we have no means of knowing definitely. Present relative elevations can not be relied upon as safe evidence. It is probable, however, that it was not far from the close of the rise, as other-wise the bed of the cañon, under the crest of the plateau, rising more rapidly than at any other point, would be the highest point, and the divide would be there instead of being several miles farther east.

Altogether, this phenomenon affords a very interesting study for the structural geologist and the geographer.

By W. H. PREECE, F. R. S.

LAST week, when we had the pleasure of meeting, I endeavored to disabuse your minds of any such idea as that electricity was a fluid, or, in fact, any kind of matter. I pointed out to you that every electric phenomenon really was a form of that curious, mysterious agency that exists throughout nature, that produces all the work done on the face of the earth, that probably is at the root of life itself, called energy. Nevertheless, we can speak of electricity as though it were a distinct entity; precisely in the same way that we speak of sound, of light, and of heat. We know that sound and heat are not sensible to the touch, or taste, or sight; so electricity is of the same character, and is invisible and insensible in every shape or form. Moreover, we can not either create or produce energy; there is only a certain fixed quantity of energy in the universe, and all that we can do is simply to transform it into its different shapes, such as I illustrated to you last week. All physical phenomena, without a single exception, may be traced to the mere transformation of this energy. I showed you on the last occasion how, by simply winding a wire round a mass of iron, and sending a current of electricity through the wire, we could produce that form of energy called electro-magnetism. To-night I have to speak of one or two other forms in which this energy does its work—forms in which, when electricity is transferred through matter, it does work in some shape or another. The operation of the electric current, when passed through chemical compounds in solution or liquid, is to tear asunder the constituents of the compound, and to arrange them on different sides. A simple means of illustrating this is a glass jar, like the one before you, containing water and two glass tubes, each fitted with a stop-cock. When an electric current is passed through

  1. Lecture delivered before the Society of Arts, January 4, 1882, and reprinted from the journal of the society.