Electrical Researches by Be la Hive and Gassiot. 33 



the magnetic poles ; it does not vary if the part of the discharge 

 near the positive electrode is near the poles, and it diminishes 

 from 30 3 to 25° if the middle of the luminous column is sub- 

 mitted to the action of the electro-magnet. This effect is evi- 

 dently due to the concentration produced by the magnet in the 

 obscure portion of the column, for the medium in becoming 

 more dense grows luminous at the same time. 1 " 



Another point on which M. de la Rive touches, is the 

 " action exerted by magnetism when the electric discharge 

 takes place in a gaseous medium, between the extremity of a 

 magnetized bar of soft iron and a circle of which its extremity 

 is the centre. At a certain degree of rarefaction the electri- 

 city manifests itself in the form of a luminous jet, which tarns 

 like the hand of a watch with great regularity, and a velocity 

 which may reach one hundred turns a minute. The direction of 

 the rotation depends on that of the magnetization, and on the 

 direction of the current ; but if a change in the direction of 

 the magnetization only modifies the direction of the rotation 

 without altering its velocity, a change in the direction of the 

 current modifies both the direction and the swiftness of the 

 rotation. This swiftness is always less when the circle forms 

 the negative electrode than when it forms the positive, which 

 probably arises from a greater friction that results from the 

 spread of the jet over the surface of the circle. The differ- 

 ence $£ velocity is much greater when the medium is more 

 rarefied, and the spreading (epanouissement) of the jet from 

 the negative electrode is more considerable with air impreg- 

 nated with vapour, there being in one minute at a pressure of — 



Pressure in millimeters. 



Circle positive. 



Circle negative. 



8 



100 turns 



52 turns 



10 



72 „ 



46 „ 



12 



62 „ 



44 „ 



At a certain degree of rarefaction the presence of vapour 

 causes the jet to divide into several jets instead of spreading, 

 and then to revolve like the spokes of a wheel. M. de la Rive 

 ascribes this to a difference of molecular arrangement in air and 

 in vapour.* 



Thus far M. de la Rive, who does not seem to have made 

 himself acquainted with the important paper on Stratified Dis- 

 charges, communicated by Mr. Gassiot to the Royal Society 

 in 1862, and which was briefly noticed by us in our April 

 number. 



Mr. Gassiot's experiments were made with an insulated 

 voltaic battery of 3360 cells. The stratified discharge was 

 in appearance precisely the same as that obtained from the in- 



* For further details see Comptes Rendus, April 13, 18G3. 

 VOL. IV. — NO. I. D 



