Page:The fairy tales of science.djvu/39

 These discoveries enabled man to employ the Amber Spirit as a courier, a vocation for which he is eminently suited, as the speed at which he travels has been estimated at 288,000 miles in a second.

Let us see how our messages may be conveyed.

In London we have a pile of zinc and copper disks, or what amounts to the same thing, an arrangement of metal plates and acids which we call a battery. We have only to connect the extremities of this machine by means of a wire to set the Amber Spirit in motion, and he will continue to move as long as the connexion remains complete, but will stop the instant it is broken. His route is from the zinc to the copper through the acid solution, and along the wire back again to the zinc. He will never leave the battery at one end unless he is quite satisfied that he can re-enter it at the other, but while there is nothing to obstruct his course he will continue to circulate through the arrangement without exhibiting the least sign of fatigue.

Let the wire which connects the opposite ends of the battery be long enough to reach to Edinburgh and back; and at the northern capital let there be a mariner's compass placed so that the needle shall be directly below, and parallel to the wire. It is evident that with this simple apparatus we can compel our courier to travel to Scotland and back. Every time we connect the homeward wire with the zinc end of the battery, the Spirit will rush to