5.26 Prof. De la Rive on the Action of Magnetism upon 



At 4 millims. pressure, the ring being positive, the number of 

 turns in 15 seconds was 36 in one jar and 38 in the other. 



Keeping the two jars in the circuit one after the other, and 

 varying the rarefaction in one of them without changing it in 

 the other, the following results were obtained : — 



The pressure in one jar being kept constant at 14 millims., 

 the rate of rotation was 14 turns in 15 seconds with the ring posi- 

 tive and 12 with the ring negative. This rate increased a little 

 when the air in the second jar was rarefied as far as 4 millims., 

 but was still only 16 and 13 turns in 15 seconds with the ring 

 respectively positive and negative : this slight increase was evi- 

 dently due to the greater intensity of the electric discharge con- 

 sequent upon the diminution of resistance in the jar in which the 

 pressure of the air was varied. As to this latter jar, the rate of 

 rotation increased in it considerably as the pressure was dimi- 

 nished, as may be seen from the following Table : — 



Pressure. 



Number of turns in 15 seconds. 



Ring positive. 



Ring negative. 



millims. 



10 



8 



6 



4 



3 



16 



20 



24 



33 

 J Too great to 1 

 \ be counted. J 



12 

 16 

 20 



22 



30 



These two jars being still used, the air in one of them was 

 rarefied as far as possible and aqueous vapour was then intro- 

 duced into it, while the other was filled with very dry air at 10, 

 12, or 14 millims. pressure. As long as the pressure of the 

 vapour was below that of the air, the rotation in it was the more 

 rapid. It rapidly diminishes when the pressure increases beyond 

 4 millims., at which point it is 33 turns in 15 seconds with the 

 ring positive, and 20 with the ring negative. At 6 millims. 

 pressure the rotations were respectively 26 and 15 ; at 12 mil- 

 lims. they were 16 and 12; and in the second jar, containing 

 air at 12 millims., they were likewise 16 and 12. It seems to 

 follow from this that, when the elastic force is the same, the rate 

 of rotation is the same in air and in aqueous vapour. 



In order to make quite sure that this was the case, I replaced 

 both jars parallel to each other in the circuit, so that the discharge 

 was obliged to divide itself between them, and began by trying 

 to what degree of rarefaction it was needful to reduce air in order 

 that its resistance might be equal to that of aqueous vapour of. a 

 certain pressure. I thus found that air at 7 millims. had the 



