202 



Prof. J. Henry's Contributio7is 



into a ring of larger diameter, as is shown in fig. 4, Sec- 

 tion III. 



Fig. 1. 



a represents coil No. 1, b coil No. 2, and c coil No. 3; e the battery, 

 c? the rasp. 



7. Coil No. 2. is also formed of copper plate, of the same 

 width and thickness as coil No. 1 . It is, however, only sixty 

 feet long. Its form is shown at b, fig. 1 . The opening at 

 the centre is sufficient to admit helix No. 1. Coils Nos, 3, 

 4, 5, 6, &c. are all about sixty feet long, and of copper plate 

 of the same thickness, but of half the width of coil No. 1. 



8. HeHx No. 1. consists of sixteen hundred and sixty yards 

 of copper wire, ^^gth of an inch in diameter; No. 2, of nine 

 hundred and ninety yards; and No. 3, of three hundred and 



Fig. 2. 



a represents helix No. 1, b helix No. 2, c helix No. 3. 



fifty yards, of the same wire. These helices are shown in 

 fig. 2, and are so adjusted in size as to fit into each other ; thus 

 forming one long helix of three thousand yards: or, by using 

 them separately, and in different combinations, seven helices 

 of diffesent lengths. The wire is covered with cotton thread, 

 saturated with bees-wax, and between each stratum of spires 

 a coating of silk is interposed. 



9. Helix No. 4 is shown at a, fig. 4, Section III. ; it is 



