﻿THE MAGNETIC TELEGRAPH. 



31 



SIGNAL KEY. - - This instru- 

 ment is generally employed to 

 make the various contacts, dif- 

 fering in succession and length, 

 by which each letter is known. 

 The fingers of the operator are 

 seen resting upon a knob at- 

 tached to a metallic spring. By 

 pressing this knob downwards, it 

 is brought upon a metallic conductor connected with a screw-cup 

 upon the right hand end of the instrument. The screw-cup upon 

 the left hand end is connected with the spring itself. One of the 

 wires from the battery passes into the first screw-cup. The other 

 screw-cup receives one of the wires of the telegraph, which proceeds 

 to the recording apparatus at the other station. By the other tele- 

 graphic wire, the remaining extremities of the battery and of the 

 recording apparatus are connected. The circuit is therefore com- 

 pleted by depressing the knob, and immediately broken when the 

 fingers are removed. 



All the curious magnetic apparatus which I have mentioned, 

 besides a great variety of other instruments, magnets, electrical ma- 

 chines, and the like, you can find at the store of Palmer and Hall, 

 at number 526 Washington street, Boston. I have lately spent 

 several hours in examining his various contrivances for testing the 

 power of electricity, some of which I will hereafter explain to you 

 and I can assure you that, old as I am, I gained a great deal of 

 highly interesting and valuable information. 



I have thus, step by step, explained the various parts of the mag- 

 netic telegraph. Do you understand it? If so, we will now pro- 

 ceed to put our machine together. We will suppose that the battery 

 and the signal key are in Boston, and that the recording apparatus 

 is in New York. One wire, from the battery, is attached to the 

 signal key. From the other end of the key, it passes upon the posts, 

 over hill and vale, across rivers and plains, to the registering appa- 

 ratus in New York, and back again to the battery in Boston. What 

 a long distance the fluid goes to get across from one plate in the 

 battery to the other, to be sure ! 



