218 MEMORIAL OF JOSEPH HENRY. 



"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 mul- 

 tiplying the number of wires, without increasing the length of each. 

 The multiplication of the wires increases the power in two ways: 

 first, by conducting a greater quantity of galvanism, and secondly, 

 by giving it a more proper direction ; for since the action of a gal- 

 vanic current is directly at right angles to the axis of a magnetic 

 needle, by using several shorter wires we can wind one on each inch 

 of tlie length of the bar to be magnetized, so that the magnetism of 

 each inch will be developed by a separate wire. In this Avay 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 great- 

 est possible. This principle is of much greater importance when 

 large bars are used. The advantage of a greater conducting power 

 from using several wires might in a less degree be obtained by sub- 

 stituting for them one large wire of equal sectional area ; but in this 

 case the obliquity of the spiral would be much greater, and conse- 

 quently the magnetic action less." * 



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 horse-shoe 9 inches 

 high ; (the sharp edges of the bar being first a little rounded by the 

 hammer;) it weighed 21 pounds. A piece of iron from the same 

 bar, weighing 7 pounds, 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 surface of the armature. Around this 

 horse-shoe 540 feet of copper bell-wire were wound 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 principle before 

 mentioned) occupied about two inches, and was coiled several times 

 backward and forward over itself. The several ends of the wires 



♦Silliman's Am. Journal of Science, Jan. 1831, vol. xix.p. -102. The three names— 

 Arago, Sturgeon, and Hknry, — may well typify the infancy, the youth, and the 

 mature manhood, of the electro-magnet. 



