404 JEtectro-Magnetic Experiments. 



it may, the fact, that the magnetic action of a current from a trough is, 

 at least, not sensibly diminished by passing through a long wire, is di- 

 rectly applicable to Mr. Barlow's project of forming an electro-mag- 

 netic telegraph, and also of material consequence in the construction 

 of the galvanic coil. From these experiments, it is evident that in 

 forming the coil we may either use onevery long wire or several shorter 

 ones as the circumstances may require ; in the first case, our galvanic 

 combinations must consist of a number of plates so as to give projec- 

 tile force ; in the second, it m,ust be formed of a single pair. 



In order to test on a large scale, the truth of these preliminary re- 

 sults, a bar of soft iron, 2 inches square and 20 inches long, wa& bent 

 into the form of a horse-shoe, 9} inches high, the sharp edges of the 

 bar were first a little rounded by the hammer, it weighed 21 lbs. ; a 

 piece of iron from the same bar weighing 7 lbs. was filed perfectly 

 flat on one surface for an armature or lifter ; the extremities of the 

 legs of the horse-shoe were also truly ground to the sui'face of the 

 armature : around this horse-shoe 540 feet of copper bell wire were 

 wound in 9 coils of 60 feet each; these coils Avere not continued 

 around the whole length of the bar, but each strand of wire, accord- 

 ing to the principle before mentioned, occvipied about two inches and 

 was coiled several times backward and forward over itself; the several 

 ends of the wires were left projecting and all numbered, so that the 

 first and the last end of each strand might be readily distinguished. 

 In this manner, we formed an experimental magnet on a large scale, 

 with which several combinations of wire could be made by merely 

 uniting the difierent projecting ends. Thus, if the second end of the 

 first wire be soldered to the first end of the second wire, and so on 

 through all the series, the whole will form a continued coil of one 

 long Avire. By soldering different ends, the Avhole may be formed into 

 a double coil of half the length, or into a triple coil of one third the 

 length, &c. The horse-shoe was suspended in a strong rectangular 

 wooden frame 3 feet 9 inches high and 20 inches wide, an iron bar 

 was fixed below the magnet so as to act as a lever of the second or- 

 der ; the different weights supported, v/ere estimated by a sliding 

 weight in the same manner as with a common steelyard. See the 

 sketch of the magnet. 



In the experiments immediately following,* a small single battery 

 was used, consisting of two concentric copper cylinders, Avith zinc be- 

 tween them ; the whole amount of zinc surface exposed to the acid 

 from both sides of the zinc Avas f of a square foot ; the battery re- 

 quired only half a pint of dilute acid for its submersion. 



Exp. 8. Each Avire of the horse-shoe Avas soldei-ed to the battery 

 in succession, one at a time ; the magnetism developed by each was 

 just sufficient to support the weight of the armature, Aveighing 7 lbs. 



^ All the weights in this series of experiments are avoirdupois. 



