Intelligence and Miscellaneous Articles. 79 



pinges on the earth amounts to one-hundredth of its gravity towards 

 the sun ; so that, if any part of it acted centrifugally, the orbit 

 would be disturbed. The same remark apphes to a comet ; but it 

 cannot be denied that the phsenomena of the tail, more especially as 

 it turns sharp round in the perihelion passage, are such as require 

 for their explanation a very active exhibition of such a centrifugal 

 force as might be engendered by the conversion of heat acting upon 

 single and free molecules. — Proceedings of the Royal Astronomical 

 Society, vol. xix. p. 29. 



ON THE DIFFERENCE PRESENTED BY THE PRISMATIC SPECTRUM 

 OF THE ELECTRIC LIGHT IN VACUO AT THE POSITIVE AND NE- 

 GATIVE POLES. BY PROFESSOR DOVE. 

 If I am not mistaken, M. Quet was the first to observe that when 

 as perfect a vacuum as possible is produced in the electric egg, and 

 the wires which enter it are connected with a RuhmkorfF's appa- 

 ratus, two lights, differing in colour, form, and position, make their 

 appearance upon these wires. One of them is blue, and uniformly 

 envelopes the negative pole ; the second, which is of a fiery-red 

 colour, adheres to the positive pole, and stretches thence towards 

 the negative pole, but is separated from the light of the latter by an 

 obscure space. These phsenomena may be studied more conveniently 

 by soldering the wires into vacuum-tubes, such as M. Geissler of 

 Bonn prepares with much skill. 



If the two lights be observed by absorption in coloured glasses, 

 or by malcing them illuminate colouring matters, it is seen immedi- 

 ately that we have not to do here with homogeneous light, for both 

 of them may be seen through a cobalt glass of 6 millims. in thick- 

 ness ; all the space which they occupy appears red through a red 

 lens, yellowish through a plate of yellow glass ; and they acquire a 

 brownish tint when looked at through a plate of uranium glass which 

 becomes fluorescent under their influence, whilst it appears porcel- 

 lanous when the electric light at its outer surface is combined by 

 reflexion with the fluorescent light proceeding from its interior. 

 These two lights vanish by the combination of a cobalt glass and a 

 red glass, which only allows the passage of the extreme homogeneous 

 red. It is easy to recognize by their colour several colouring mat- 

 ters when they are illuminated by the positive or negative light. 



If the light be allowed to pass through a narrow fissure, and ana- 

 lysed with an equilateral prism of flint glass or sulphuret of carbon, 

 the positive and negative lights furnish diflferent spectra. 



A Gcisslcr's tube, of a pear-shape, 7 inches in length, presented 

 the following pha3nomcna : — The spectrum of the blue light at the 

 negative ])ole showed a large black streak in the blue, and a second 

 similar one at the limits of the blue and green, a very small streak 

 at the limits of the yellow, and nothing in the red. The light of the 

 positive i)ole gave a continuous violet and blue band, several small 

 streaks in the green, a very black streak at the limits of the yellow, 

 and a small dark streak in the middle of the red. The colours which 

 appear discontinuous in one s])ectrum are not so in the other. 



