Scientific Lectures. 185 



that on the land lines. The gutta percha covering of the copper 

 wires, nuder the pressure of a great depth of water, becomes an 

 absorbent of the electricity which is being sent throngh them to the 

 extent of ninety per cent. The first portion of the electric wave of 

 ten per cent crosses the ocean (1,700 miles) in two seconds, and it 

 would be followed by a succession of waves from the restoration of 

 that portion of the electricity which has been absorbed by the gutta 

 percha in impulses, and the signal would be repeated like echoes, and 

 produce not only confusion, but great delay. To remedy this, Pro- 

 fessor Varley introduced a key, which sends alternate currents, posi- 

 tive and negative, at such intervals as allow the first wave of ten per 

 cent to pass forward, and then that portion absorbed by the covering 

 is neutralized by its opposite, and the cable is cleared for the trans- 

 mission of a second pair of currents. The battery used is a very 

 email one (three of Daniels' cups), and the signal, being only ten per 

 cent of this small current, is powerless to move any of the other 

 instruments in use on land. The instrument used consists of a minute 

 polarized needle, suspended on a single strand of a spider's web, or 

 one from the silk worm. In the middle of this minute needle is 

 placed an almost microscopic mirror, which reflects a single ray of 

 light from a powerful lamp. The currents of electricity deflect this 

 needle alternately to the right and left for a space of time correspond- 

 ing to that occupied in the signal on the land line, the same kind of 

 alphabet being used in both cases. The receiver (not operator) site 

 in a dark room, and the small mirror reflects the ray of light upon a 

 piece of white paper before him, on which a black line is dravsai, to 

 the right and left of which the light is alternately reflected.. The 

 receiver reads these signals by " sight," and transmits them to another 

 person, placed outside of the dark room, by means of an ordinary 

 instrument. A short time since. Gen. Reynolds told me that he had 

 Bent a message, without either a wire or a cable, ninely-two miles, 

 across an arm of Lake Superior, by means of the Heliotrope or 

 mirror, and on the return of his messenger (who had l)een sent 

 with a written copy), he found that the Heliotrope mes- 

 sage had been received, understood and obeyed. He had 

 two assistants, who had been telegraphic operators, who had for tlie 

 whole summer been amusing themselves in talking to each other with 

 these instruments, though they were stationed ten, twentj^, or thirty 

 miles apart. When the rebel Gen. Morgan made . his great raid 

 through Indiana and Ohio, he captured one of my operators, and 



