110 PROCEEDINGS OF THE EEGENTS. 



battery occupying about a cubic foot of space. It consists of tbirty 

 strands of wire, each about forty feet in length. 



The abovementioned experiments exhibit the important fact that 

 when a galvanic battery of intensity (that is to say, a battery con- 

 sisting of a number of pairs) is employed, the electro-magnet con- 

 nected with it must be wound with one long wire, in order to produce 

 the greatest effect ; and that when a battery of quantity, (that is, one 

 of a single pair,) is employed, the proper form of the magnet con- 

 nected with it is that in which several shorter wires are w^ound around 

 the iron. The first of these magnets, which is the one now employed 

 in the long or main circuit of the telegraph, 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 circum- 

 stances, exceedingly small, and in order that this may develop mag- 

 netism 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 along single coil. Hence it will be seen 

 that the electro-magnet of Mr. Sturgeon was not applicable to tele- 

 graphic purposes in a long circuit. 



Previous to making the last experiments abovementioned, in order 

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

 the conduction of wires of different lengths and diameters, with dif- 

 ferent batteries. In these experiments a galvanometer, or aa instru- 

 ment consisting of a magnetic needle freely suspended within a coil 

 of wire, was first employed to denote, by the deflectioa 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, tbat 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 subslituttd in its place. With a single battery, the same 

 result was again obtained — a great diminution of lifting power with 

 the increase of distance. After this the battery of a single pair was 

 removed and its place supi)lied by one ot 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 tele- 

 graph was now practicable ; and, in publishing my experimenis 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 ot 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 



