392 MEMORIAL OF JOSEPH HENRY. 



the liolc M'as exjwsed sufficiently to separate the 'poles' one-third 

 of an inch. Another piece of iron also eight inches long was then 

 })laned, and being secured with its face in contact with the other 

 planed surface, the whole was turned into a cylinder eight inches 

 long, three inches and three-quarters in exterior — and one inch 

 interior diameter. The larger piece was then covered with calico, 

 and wound with four coj)per wires (covered with silk) each 23 feet 

 long and one-eleventh of an inch in diameter; — a quantity which 

 was just sufficient to hide the exterior surface, and entirely to fill 

 the inside hole."* This magnet weighing without wire but 15 

 pounds, lifted 2,090 pounds. 



Joule subsequently made another magnet still deeper, or longer in 

 its tubular extent ; the grooved iron with its closed armature being 

 not unlike a gun-barrel. The length of this soft-iron cylinder was 

 two feet; its external diameter about one inch and a half, and its 

 internal diameter a half inch : the weight of the grooved magnet 

 being 6 pounds 11 ounces, and that of its armature, 3 pounds 7 

 ounces. A copper rod three-eighths of an inch thick was bent once 

 around each side of the tube, or elongated pole. With a battery of 

 8 cells of two square feet each (16 sc^uare feet) arranged as a single 

 pair, a lifting power of 1,350 pounds was induced. The single thick 

 copper rod having then been replaced with a bundle of 60 copper 

 wires, each one-twenty-fifth of an inch thick, the magnet lifted 

 1,856 pounds. This remarkable success of the ''multiple coil" led 

 Joule to increase the number of coils in the former tube-like magnet. 

 The four wires each one-eleventh of an inc^h thick were replaced by 

 twenty-one wires of the same length, each one-twenty-fifth of an 

 inch thick, the whole being bound together by cotton tape. " Six- 

 teen cast-iron cells of the same size as those jireviously described, 

 [each of two square feet,] were then arranged in a series of four, 

 and connected by sufficiently good conductors to the electro-magnet. 

 The ])ower which was then necessary to break it from its armature, 

 was 2,775 pounds, or nearly a ton and a quarter. An inuiiense 

 weight, when it is considered that the whole apparatus — magnet 

 armature and coils — weighs less than 26 pounds." f 



♦sturgeon's Annals of Electrici/i/, oto. Sept. 18-10, vol. v. i^p. 190, 101. A second 

 much smaller magnet of similar form, Ijeing 2.7 inches long, and half an inch in 

 diameter, wrapped AVith 7 feet of insulated copper wire one-twentieth of an inch 

 thick, and weighing 1,0.57 grains, (somewhat over two ounces,) lifted 49 pounds. A 

 third magnet elliptical in form (0.37 inch broad and 0.15 inch thick) 0.7 inch long, 

 covered with 19 inches of copper wire one-fortieth of an inch thick, and weighing 

 6.5.3 grains, lifted 12 pounds. And a fourth magnet one twenty-tifth of an inch 

 thick and one-quarter of an inch long, with tliree turns of line copper wire, 

 weighing half a grain, lifted 1,117 grains. 



t Sturgeon's Annals of Electricity, Dec. 1840, vol. v. pp. 471, 472. 



