Page:Popular Science Monthly Volume 9.djvu/356

 334 of induction gives you over these wonderful and complicated phenomena. By those principles the various facts of our science are bound together to an organic whole. But we have not yet exhausted the fruitfulness of this principle.

Consider the following problem. Usually we allow the electricity of the outer coating to escape to the earth. Suppose we try to utilize it. Place, then, your jar upon vulcanized India-rubber, and connect its outer coating by a wire with the knob or inner coating of a second jar. What will occur when the first jar is charged? Why, the second one will be charged also by the electricity which has escaped from the outer coating of the first. And suppose you connect the outer coating of the second insulated jar with the inner coating of a third; what occurs? The third jar will obviously be charged with the electricity repelled from the outer coating of the second. Of course, we need not stop here. We may have a long series of insulated jars, the outer coating of each being connected with the inner coating of the next succeeding one. Connect the outer coating of the last jar with the earth, and charge the first jar. You charge thereby the entire series of jars. In this simple way you master practically, and grasp the theory of the celebrated "cascade battery" of Franklin, represented in Fig. 26, with coated glass tumblers, A, B, C, D,



and so on. You must see that, before making the experiment, you could really have predicted what would occur. This power of prevision is one of the most striking characteristics of science.

. Novel Leyden-Jars of the Simplest Form.—But, possessed of its principles, we can reduce the Leyden-jar to a far simpler form than any hitherto dealt with. Spread a sheet of tin-foil smoothly upon a table, and lay upon the foil a pane of glass, somewhat smaller than the foil in size. Remember that the glass, as usual, must be dry. Stick on to the glass by sealing-wax two loops of narrow silk ribbon, by which the pane may be lifted; and then lay smoothly upon the glass a second sheet of tin-foil, less than the pane in size.