HENRY AND THE TELEGRAPH. 283 



that Tvitli a current from only two and a half square mches of zinc, the 

 magnet hekl 14 pounds.* Winding upon its arms a second wire of the 

 same length (30 feet) whose ends were similarly joined to the .same gal- 

 vanic pah', the magnet lifted 28 pounds. On these results he remarks : 



" These experiments conclusively proved that a great development of 

 magnetism could be effected by a very small galvanic element, and also 

 that the power of the coil was materially increased by multiplying the 

 number of wires, without increasing the length of each. The multi- 

 plication of the wires increases the power in two ways : first, by con- 

 ducting a greater quantity of galvanism, and secondly, by giving it a 

 more proper direction ; for since the action of a galvanic current is di- 

 rectly at right angles to the axis of a magnetic needle, by using sev- 

 ea"al shorter wires we can wind one on each inch of the length of the 

 bar to be magnetized, so that the magnetism of each inch will be dc; 

 veloped by a separate wire. In this way the action of each particular 

 coil becomes directed very nearly at right angles to the axis of the bar, 

 and consequently the effect is the greatest possible. This principle is 

 of much greater imiDortance when large bars are used. The advan- 

 tage of a greater conducting power from using several wires might in a 

 less degree be obtained by substituting for them one large wire of equal 

 sectional area ; but in this case the obliquity of the spiral would be much 

 greater, and consequently the magnetic action less."t 



But in the following year, 1830, Henry pressed forward his researches 

 to still higher results. Assisted by his friend Dr. Philip Ten-Eyck, he 

 proceeded to test the power of electro-magnetic attraction on a larger 

 scale. "A bar of soft iron 2 inches square and 20 inches long was bent 

 into the form of a horseshoe 9 J inches high; (the sharp edges of the bar 

 were first a little rounded by the hammer;) it weighed 21 pounds. A 

 piece of iron from the same bar, weighing 7 pounds, was filed i)erfectly 

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

 legs of the horse-shoe were also truly ground to the surface of the arm- 

 ature. Around this horse-shoe 510 feet of copper bell-wire were w^ound 

 in nine coils of 60 feet each ; these coils were not continued around the 

 whole length of the bar, but each strand of wire (according to the prin- 

 ciple before mentioned) occupied about two inches and was coiled sev- 

 eral times backward and forward o\er itself. The several ends of the 

 wires were left in'ojecting, and all numbered, so that the first and the 

 last end of each strand might be readily distinguished. In this man- 

 ner we formed an experimental magnet on a large scale, with which 

 several combinations of wire could be made by merely uniting the dif- 

 ferent 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 wire. By solder- 



* It must not be for;>otten that at the time Avlien this experimeutal magnet was 

 marie, the strongest electro-magnet in Europe was that of Sturgeon, capable of sup- 

 porting 'J pounds, with 130 square inches of zinc surtace in the battery. 



tSillimau 8 Am. Journal of Science, Jan. 1831, vol. xix, p. 402. 



