152 iTitelligence and Miscellaneous Articles. 



with a velocity of 102 (urns of the jet in 30 seconds — and on put- 

 ting-in the swivel, a diminution of 10° for a velocity of 22 turns of 

 the swivel and 82 turns of the jet in 30 seconds. 



With hydrogen, without the swivel the rotation induces no sen- 

 sible diminution of intensity. It must be remarked that in this case 

 the jet disappears and divides into an infinite number of threads 

 throug-hout the mass of the gas, as an ordinary electric current in a 

 liquid conductor does in the same circumstances, so that the whole 

 of the gaseous sheet turns under the action of the magnet. 



Nevertheless, before concluding from these last experiments that 

 the diminution of the intensity of the current is due to the mecha- 

 nical force exerted by the jet upon either the swivel or the gaseous 

 medium, we must take ac-count of a circumstance which may have 

 some influence on that diminution, viz. the cooling which the jet 

 undergoes in its rotation by contact with both the rotating disk and 

 the gaseous medium. In these last instances the cooling can be as- 

 certained by the manometer, which indicates a slight increase of 

 pressure when the jet is rotating ; and this can only be occasioned 

 by its coming into contact in its rotation with different parts of the 

 medium and heating it so much the more. Yet, if we compare this 

 effect with the diminution of intensity of the current, we do not find 

 a sufficient ratio to account for that influence. Thus, on employing 

 a smaller bell-glass with air under a pressure of 10 millims., we ob- 

 tain, for a velocity of 90 turns in 30 seconds, 8^ diminution of inten- 

 sity of the current (from 42° to 34°), while the increase of pres- 

 sure is only '08 of a millimetre — indicating a very slight elevation 

 of the temperature of the gaseous medium, and consequently a very 

 slight cooling of the jet. 



But more than that. If. by means of apparatus arranged for the 

 purpose, we give to the bell containing the rarefied gas and the 

 swivel a movement of rotation on its axis, there is almost no dimi- 

 nution of intensity when the apparatus is made to turn in the same 

 direction and Avith the same velocity that the magnetization gives to 

 the jet, while, in the same circumstances, the rotation given to the 

 swivel by the jet produces a diminution of the current-intensity 

 from 5° to 3^. We can even, without employing the action of the 

 magnet, communicate a rotatory motion to the sM'ivel directly, by 

 means of the rapid rotation of the bell-glass, in which it will meet 

 and cut the motionless jet several times without there resulting any 

 change in the intensity of the current. If, however, the diminution 

 were owing to the cooling of the jet effected by its contact with the 

 swivel, we ought to observe it in this case — while if it proceeds 

 from the work done upon the swivel, as there is none in this expe- 

 riment, there ought to be no diminution : now this is just what does 

 take place*. 



* The employment of the revolving table enables us to show in the most 

 direct manner that the division of the jet in its rotation under the mfluence 

 of the magnet is only an illusion, depending solely on the velocity of the 

 rotation and the continued impression resulting therefrom upon the retina. 



