202 Prof. J. Henry’s Contributions 
into a ring of larger diameter, as is shown in fig. 4, Sec- 
tion III. 
Fig. 1. 
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 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. Helix 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. 
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 different 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 
