the Electric Discharge in highly Rarefied Gaseous Media. 529 



by taking tbe jar with the iron rod off the pole of the electro- 

 magnet, and placing it at such a distance that it is not affected 

 by it, and leaving everything else as it was. 



Thus, in thel ast experiment that I have quoted, the two jars 

 being respectively on the two polar surfaces of the electro- 

 magnet, and the air in both being rarefied to 8 millims., we had 

 25 turns in a quarter of a minute in the jar with the brass rod, 

 whether the ring was positive or negative ; while in the jar 

 with the iron rod there were 46 turns in the same time when 

 the ring was positive, and 22 when it was negative. Tbe jar 

 with the iron rod having been removed from the electromagnet, 

 the numbers of turns in the other jar were 29 and 30 instead 

 of 25 as before, although the discharge still passed through the 

 jar with the iron rod; but the rod not being magnetized, there 

 was no rotation. 



This effect is sensible only when the pressure is low, as from 

 8 to 10 millims. or less, and when the ring is positive in the jar 

 with the iron rod. In all probability it is due to the following 

 cause : the soft iron being in this case the negative electrode, its 

 magnetization producing a condensation of that part of the elec- 

 tric jet near to the negative electrode, increases the resistance, 

 and thus diminishes the intensity of the discharge*. 



This effect is independent of the direction of the magnetiza- 

 tion, and depends only upon the direction of the discharge. 

 Up to a certain point, the rate of rotation of the jet in the jar 

 with the brass rod is independent of the direction of the dis- 

 charge in this jar when there is no magnetization in the other. 

 Nevertheless, when the discharge is weak, I have thought I 

 could detect, at 8 millims. (and even at 6 millims.) pressure, even 

 when the soft-iron rod in the second jar was not magnetized, a 

 difference in the rate of rotation of the jet in the jar with the 

 brass rod, according to whether the ring is positive (in which 

 case the rate of rotation is smaller), or whether it is negative (in 

 which case it is a little greater). It is unnecessary to point out 

 that this is just the contrary of what happens in the jar with 

 the magnetized iron rod. 



The effect of magnetization can likewise be rendered sensible 

 by putting into the circuit, at the same time as the jar with the 

 brass rod, an electrical egg in place of the jar with the iron rod. 

 One of the rods between which the electric jet passes in the egg 

 is made of soft iron ; and as soon as this is magnetized, if it 



* "We have already seen, at the beginning of this memoir (p. 513), the 

 great influence which the neighbourhood of a magnetic pole has upon the 

 electrical resistance of a rarefied gaseous medium, especially when the 

 pole is near the negative electrode, and the discharge is transmitted 

 through a tube. 



