392 MEMORIAL OF JOSEPH HENRY. 



the hole was exposed sufficiently to separate the 'poles 7 one-third 

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

 planed, 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 copper 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 square 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 inch 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 previously 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 power which was then necessary to break it from its armature, 

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

 weight, when it is considered that the whole apparatus magnet 

 armature and coils weighs less than 26 pounds." f 



* Sturgeon's Annals of Electricity, etc. Sept. 1840, vol. v. pp. 190, 191. A gecond 

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

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

 thick, and weighing 1,057 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 

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

 thick and one-quarter of an inch long, with three turns of fine copper wire, 

 weighing half a grain, lifted 1,417 grains. 



f Sturgeon's Annals of Electricity, Dec. 1840, vol. v. pp. 471, 472. 



