486 M. A. Bertin on Circular Magnetic Polarization. 



tion observed ought to be in the same direction, whether the 

 glass is placed in front or behind ; and if the helix is viewed 

 from the south pole, a rotation to the left should occur: it 

 would be to the right if the helix were viewed from the other 

 pole, or, which comes to the same thing, the current is changed 

 without altering the position of the eye. 



Hence it follows, that in an apparatus formed of two similar 

 helices, the direction of the rotation should be the same when 

 the flint-glass is between the two helices or reels as when it is 

 at the extremities ; so that in the whole length of a file of 

 reels thus arranged, the direction of the rotation should not 

 change. 



If, then, several glasses are placed in the intervals separa- 

 ting these reels, the rotations produced by all these glasses 

 will add to each other, and thus give the means of multiplying 

 indefinitely the action of a substance, and consequently of 

 rendering that action visible, however feeble it may be. 



All these suppositions are confirmed by experiment, as I 

 have found by means of two systems of straight reels. In 

 the one system, consisting of two reels, ^28 centimetres in 

 length, and inclosing an iron nucleus, 8 centimetres in diameter, 

 both of them in contact with the flint-glass of Faraday, of 

 48 millimetres in length, produced a rotation of nine degrees. 

 The other system, consisting of four reels 10 centimetres in 

 length, and inclosing a cylinder of 3 centimetres in diameter, 

 perforated likewise in the direction of the axis ; they are centred 

 one after the other in a wooden trough*. This file of reels, 

 including the external ones, presents five intervals in which the 

 substances submitted to magnetism may be placed. Some 

 experiments made with this apparatus are here added. 



1st. Experiment made mthjive cells containing sulphur et of 

 carbon 1 centimetre in thickness. Rotations. 



With five cells placed in the five intervals ... 8 5 



With the two outer cells removed 6 25 



With only the centre cell left 2 00 



The five cells in contact, with two reels on either"! , „^ 



side j- 4 00 



55 



2nd. Experiment on water. 



With one cell placed between the first and second 



reels 



With a second placed between the second and', , ,^ 

 third reels / ^ *^ 



* This apparatus was lent to me by M. Pouillet. 



