314 



CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



a 



^ss^ 



feet in diameter, and helix No. 

 4 placed as is shown in the 

 figure. When the helix was 

 at the distance of about sixteen 

 inches from the middle of 

 the plane of the ring, shocks 

 could be perceived through 

 the tongue, and these rapidly 

 increased in intensity as the 

 . ,, r AT ^ 7. , ;vT , . ^ r ■ helix was lowered, and when 



a represents helix JNo. 4, 6 coil No. 1, in the form of a ring. ^ 



it reached the plane of the ring 

 they were quite severe. The eflfect, however, was still greater, when 

 the helix was moved from the centre to the inner circumference, as at 

 c: but when it was placed without the ring, in contact with the outer 

 circumference, at h, the shocks were very slight; and when placed 

 within, but its axis at right angles to that of the ring, not the least 

 eflfect could be observed. 



47. With a little reflection, it will be evident that this arrangement 

 is not the most favourable for exhibiting the induction at a distance, 

 since the side of the ring, for example, at c, tends to produce a current 

 revolving in one direction in the near side of the helix, and another in 

 an opposite direction in the farther side. The resulting eflfect is there- 

 fore only the diflference of the two, and in the position as shown in the 

 figure ; this diflference must be very small, since the opposite sides of 

 the helix are approximately at the same distance from c. But the dif- 

 ference of action on the two sides constantly increases as the helix is 

 brought near the side of the ring, and becomes a maximum when the 

 two are in the position of internal contact. A helix of larger diameter 

 would therefore produce a greater eflfect. 



48. Coil No. I remaining as before, helix No. 1, which is nine 

 inches in diameter, was substituted for the small helix of the last ex- 

 periment, and with this the eflfect at a distance was much increased. 

 When coil No. 2 was added to coil No. 1, and the currents from two 

 small batteries sent through these, shocks were distinctly perceptible 

 through the tongue, when the distance of the planes of the coils and 

 the three helices, united as one, was increased to thirty-six inches. 



