31 



graph, may be called an intensity magnet ; and the second, which is 

 used in the local circuit, may be denominated the quantity. 



The quantity of electricity which can be passed through a long circuit 

 of ordinary sized wire is, under the most favorable circumstances, exceed- 

 ingly small, and in order that this may develop magnetism in a bar of 

 iron, it was necessary that it should be made to revolve many times 

 around the iron, that its effects may be multiplied ; and this is effected 

 by using a long single coil. Hence it will be seen that the electro-magnet 

 of Mr. Sturgeon was not applicable to telegraphic purposes in a long 

 circuit. 



Previous to making the last experiments above mentioned, in order to 

 guide myself, I instituted a series of preliminary experiments on the 

 conduction of wires of different lengths and diameters, with different 

 batteries. In these experiments a galvanometer, or an instrument con- 

 sisting of a magnetic needle freely suspended within a coil of wire, was 

 first employed to denote, by the deflection of its needle, the power of the 

 current. The result from a number of experiments, with a battery of a 

 single pair, was the same as that obtained by Barlow, namely, that the 

 power diminished rapidly with the increase of distance. With the same 

 battery, and a larger wire, the diminution was less. The galvanometer 

 was next removed, and a small electro-magnet substituted in its place. 

 With a single battery, the same result was again obtained — a great dim- 

 inution of lifting power with the increase of distance. After this the 

 battery of a single pair was removed and its place supplied by one of 

 intensity, consisting of twenty-five pairs. With this the important fact 

 was observed, that no perceptible diminution of the lifting power took 

 place, when the current was transmitted through an intervening wire 

 between the battery and the magnet of upwards of one thousand feet. 



This was the first discovery of the fact that a galvanic current could 

 be transmitted to a great distance with so little a diminution of force as 

 to produce mechanical effects, and of the means by which the transmission 

 could be accomplished. I saw that the electric telegraph was now prac- 

 ticable ; and, in publishing my experiments and their results, I stated 

 that the fact just mentioned was applicable to Barlow's project of such 

 a telegraph. I had not the paper of Barlow before me, and erred in 

 attributing to him a project of a telegraph, as he only disproved, as he 

 thought, the practicability of one. But the intention of the statement 

 was to show that I had established the fact that a mechanical effect could 

 be produced by the galvanic current at a great distance, operating upon 

 a magnet or needle, and that the telegraph was therefore pos^ble. In 

 arriving at these results, and announcing their applicability to the tele- 

 graph, I had not in mind any particular form of telegraph, but referred 



