On Electro-Dynamic Induction. 211 



designated by the names of coil No. 1, coil No. 2, &c. ; also of 

 several coils of long wire ; and these, to distinguish them from 

 the ribands, will be called helix No. 1, helix No. 2, &c. 



6. Coil No. 1 is formed of thirteen pounds of copper plate, one 

 inch and a half wide and ninety-three feet long. It is well cov- 

 ered with two coatings of silk, and was generally used in the 

 form represented in Fig. 1, which is that of a flat spiral, sixteen 

 inches in diameter. It was however sometimes formed into a 

 ring of larger diameter, as is shown in Fig. 4, Section III. 



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 6, Fig 1. The opening at the centre is suf- 

 ficient to admit helix No. 1. Coils No. 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. 



Fig. 2. 



h 



a helix No. 1, h helix No. 2, c helix No. 3. 



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

 copper wire, ^^th of an inch in diameter ; No. 2, of nine hun- 

 dred and ninety yards ; and No. 3, of three hundred and 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 sepa- 

 rately, 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 formed 

 of five hundred and forty-six yards of wire, ^V^h of an inch in 

 diameter, the several spires of which are insulated by a coating 

 of cement. Helix No. 5 consists of fifteen hundred yards of sil- 

 vered copper wire, yisth of an inch in diameter, covered with 

 cotton, and is of the form of No. 4. 



10. Besides these I was favored with the loan of a large spool 

 of copper wire, covered with cotton, -f'^th of an inch in diameter, 



