200 Mr. W. Sturgeon ofi Electw-Magnefs. 



are separate from each other 1 ^ inch ; the cross piece whicli 

 joins the poles is from the same rod of iron, and about y| 

 inches long. 



Twenty separate strands of copper wire, each strand about 

 50 feet in length, are coiled round the iron one above another, 

 from pole to pole, and separated from each other by inter- 

 vening cases of silk ; the first coil is only the thickness of 

 one ply of silk from the iron, the twentieth or outermost 

 about half an inch distant from it. By this means the wires 

 are completely insulated from each other without the trou- 

 ble of covering them with thread or varnish. The ends of 

 the wires project about two feet, for the convenience of con- 

 nection. 



With one of my small cylindrical batteries, exposing about 

 150 square inches of total surface, this electro-magnet supports 

 400 pounds. I have tried it with a larger battery, but its ener- 

 gies do not appear to be so materially exalted as might have 

 been expected by increasing the extent of galvanic surface. 

 Much depends upon a proper acid solution : good nitric or ni- 

 trous acid, with about six or eight times its quantity of water, 

 answers very well. M^ith a new battery of the above dimensions, 

 and a strong solution of salt and water at a temperature of about 

 190° Fahr., the electro-magnet supported between 70 and 80 

 pounds, when the first 1 7 coils only were in the circuit. With 

 the three exterior coils alone in the circuit, it would just sup- 

 port the lifter or cross piece. When the temperature of the 

 solution was between 4'0° and 50°, the magnetic force excited 

 was comparatively very feeble. With the innermost coil alone, 

 and a strong acid solution, this electro-magnet supports about 

 100 pounds : with the four innermost wires, about 250 pounds. 

 It improves in power with every additional coil until about the 

 twelfth, but not perceptibly any further: therefore the re- 

 maining eight coils appear to be entirely useless ; although 

 the last three of them, independent of the innermost seventeen, 

 and at the distance of half an inch from the iron, produce in 

 it a lifting power of 75 pounds. 



It is evident from these results, that the exciting power of 

 this miniature battery becomes improved by multiplying the 

 number of conducting wires as iar as twelve at least, although 

 thegreater part of them be at some considerable distance from 

 the ii'on; and it is highly probable, although the experiments 

 which I have made on this bar do not satisfactorily prove the 

 fact, that by employing a larger galvanic surface, a much 

 further addition to the number of conducting wires may be 

 advantageously introduced into the circuit for the excitation of 



the 



