1S8 PHENOMENA ACCOMPANYING 



I liave mule many exporimcnt? with this jar by filling it successively with 

 atmospheric air, with nitrogen, and with hydrogen, at difterent degrees of rare- 

 faction, these gases being at times perfectly dry ; at others, containing a greater 

 or less proi)ortion of vapor, either of water or of alcohol. 



Atmospheric air and nitrogen, when both dry, give nearly identical results, 

 with this ditferencc, that the light is more vivid and clearer with nitrogen. If 

 the soft iron be taken for the positive electrode, and the ring for the negative 

 one, the luminous current is seen to form, at a certain degree of rarefaction, a 

 sort of peac'h-red envelope around the top of the soft iron, and a sheath of a 

 pale violet color along an arc of a greater or less number of degrees around the 

 ring. At a very weak pressure this sheath encompasses the whole ring, while 

 the to]i of the soft iron is completely enveloped with a rose-colored aureole, 

 from which issues a very short stream of the same shade, and presenting the 

 form of a large virgule, or comma. This virgule, when the iron is magnetized, 

 is distinctly seen to turn in one or the other direction,. with the aureole from 

 which it fuianates, according to the direction of the magnetization. The violet- 

 colored slieath which surrounds the ring is also seen to turn in the same direc- 

 tion with the rose-colored aureole, although they are separated by a space 

 complcicly obscure. By changing the direction of the discharges, there will be 

 seen at the negative electrode a violet-colored envelope, which only covers the 

 whole surface of the top of the iron rod when the gas is very much rarefied, and 

 at the positive electrode, brilliant points, separated from one another by a roseate 

 glimmer which surrounds the entire ring, and whence emanate regular stratifi- 

 cations, internally concentric to the ring. When the gas is not greatly rarefied, 

 theie is seen to issue from the ring a luminous jet which tends to the summit 

 of the central rod of soft iron, being only separated from it by a small, black 

 space, and which undergoes a movement of rotation in one direction or the 

 other, like the hand of a watch, according to the direction of the magnetization. 

 In this case there is but a portion of the top of the iron rod which is covered 

 with the violet envelope, and thia luminous segment turns with the brilliant jet. 



I have made a great number of experiments, under the conditions just indi- 

 cated, with atmospheric air, with nitrogen, and with hydrogen, Avhether dry or 

 more or less charged with vapors. I shall proceed to give a description of them 

 in a summary manner, first remarking, however, that, whatever be the gas and 

 its degree of elasticity, whether it be dry or impregnated with vapor, the rapidity 

 of rotation is always much greater when the ring serves as the positive than 

 when it serves as negative electrode, and that this rotation, which increases in 

 rapidity in proportion as the tension diminishes, ceases to be appreciable at a 

 much less tension in the second case than in the first. 



In my earlier experiments I had made use of a large globe, twentj^-five cen- 

 timetres in diameter, in which the ring was twenty centimetres in diameter, 

 and the central iron rod three. This globe was furnished with two tubulures, 

 one serving to introduce the iron rod,, whose top reached the centre of the 

 globe, and its lower extremity issuing from the tubulure, so as to be capable of 

 resting on the polar surface of an electro-magnet. The other tubulure was 

 closed by acock, which served to introduce the gas and vapor, and from it there 

 issued an isolated conductor, which supported the ring and admitted of its being 

 jdaced in the circuit. The discharge thus passed between the summit of. the 

 rod of soft iron and the metallic ring. 



This globe was^ filled with air rarefied to 4'"™. The discharge took place 

 under the form of a stream which turned with a rapidity of sixty revolutions 

 per minute when the ring was positive, and twenty Avheu it was negative. At 

 a pressure of C"™ the velocity was only forty revolntions per second in the 

 ibrmer case and twenty in the latter. With vapor of alcohol, at a pressure of 

 .')"»■', the velocity was respectively twenty-two and eleven revolutions per minute. 



