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





Number of turns in one minute. 



Pressure. 







Ring positive. 



Ring negative. 



millims. 







2 







4 







6 





92 



8 



140 



70 



10 



120 



52 



12 



90 



50 



14 



80 



48 



It will be seen that at equal pressures the rotation is more 

 rapid in presence of aqueous vapour than with dry air, — a fact 

 which is probably connected with the greater facility with which 

 the discharge is transmitted. When the external air is of a me- 

 dium degree of humidity, we have at a pressure of 14 millims. 

 72 turns instead of 80 with the ring positive, and 44 instead of 

 48 when the ring is negative. 



But the most characteristic fact which the presence of aqueous 

 vapour brought out was the division of a single electrical jet 

 under the influence of magnetism into a series of small, distinct, 

 equidistant jets which turn like the spokes of a wheel. This 

 division can be seen only when the ring serves as positive elec- 

 trode. At a pressure of 6 millims. the single jet begins to ro- 

 tate, and afterwards spreads out and the rotation is no longer 

 sensible; but under pressures of 8, 10, and 12 millims. the jet di- 

 vides itself under the action of magnetism, as soon as the rotation 

 begins, into five or six jets, which turn, as we have already said, 

 like the spokes of a wheel; whereas when the air is dry the jet 

 never divides itself, but merely spreads out at low pressures into 

 a sector or a circle, the whole of which is continuous throughout. 



When the ring is negative, it will be observed that, in pre- 

 sence of vapour, the jet which starts from the summit of the 

 soft-iron rod exhibits at the part where it is in contact with the 

 iron, at the moment when the iron is magnetized, instead of a 

 continuous surface, a series of bright points which seem to be 

 the starting-points of an equal number of small jets not sepa- 

 rated from each other far enough to be distinct. It is thus 

 simply an expansion or spreading out which is undergone by 

 the part of the jet which is in contact w T ith the iron, and the 

 jet does not divide itself into several veins. 



Alcohol-vapour produces exactly the same effect as aqueous 

 vapour. The single jet is much more brilliant in this case than 

 it is with dry air or with aqueous vapour : it exhibits beautiful 

 stratifications which give to it exactly the appearance of a che- 

 nille. Magnetization causes it to spread out and to divide into 



