324 Intelligence and Miscellaneous Articles. 



subsidence produces solenoidal currents, which may help to explain 

 the equality of i\, v.. and v.,. 



ON THE APPEARANCES OF THE ELECTRIC ARC IN THE VAPOUR OF 

 BISULPHIDE OF CARBON. BY M. JAMLN, WITH THE ASSISTANCE 

 OF M. G. 3IANEUYRIER. 



At the meeting of the 19th June I made known to the Academy 

 the modifications undergone by the electric arc in the vacuum of 

 an air-pump when the arc is produced by a Gramme machine with 

 alternating currents of high tension. I soon perceived that the 

 appearances are modified it" gases or vapours are introduced into 

 the glass vessel in which the experiment is made. In the vapour 

 of bisulphide of carbon they are very remarkable. 



The burner is formed by two parallel vertical carbons fixed at 

 their bases ; the upper extremities, which face each other, can by a 

 simple mechanism be joined or separated. The apparatus is placed 

 under a large receiver of an air-pump, in which a vacuum as com- 

 plete as possible is produced. It is known that then the arc is not 

 formed : it is replaced by the gleams of a Geissler tube ; but when 

 a few drops of bisulphide of carbon are introduced, so as to obtain 

 an increase of pressure of 5 or 6 centiin., the arc is seen to kindle 

 between the points when they touch, and to persist after they are 

 separated. 



At that moment there is as it were an explosion of light, so vivid 

 as to be insupportable, incomparably superior to the usual bright- 

 ness of the arc. On looking at it through a dark-coloured glass, 

 one sees a brilliant arc 5 or 6 centim. in height, resembling a horse- 

 shoe or a capital omega. The two extremities are at the two 

 carbon points. Besides this a long flame is seen like that of a 

 hearth, which overhangs the arc, escapes from it, and ascends ver- 

 tically. 



The points of the carbons appear red and very brilliant ; but the 

 arc is pale green ; and as its light dominates that of the carbon?, 

 the whole room is illuminated with that tint, as it would be by a 

 Bengal light with copper. The brightness increases with the 

 increase of tension of the vapour, until it becomes intolerable ; but 

 as the resistance of the medium is augmented at the same time, the 

 arc often goes out, and it is necessary to relight it every moment 

 by joining the two carbons. 



Examined with the spectroscope this light presents all the lines 

 of carburetted gases in combustion, but more complete and sharper. 

 They are those described by M. Thollon at the meeting on August 1, 

 1881. The spectrum is very discontinuous. At its red end a 

 grooved region was seen — first a very bright line followed by several 

 others thinner and close, then a broader Hue a repetition of the 

 first and likewise followed by fine lines ; these appearances were 

 repeated in going towards the orange, but growing weaker till they 

 disappeared. After a dark interval the same appearances were 

 seen again in the yellow and the beginning of the green ; then there 



