Notices respecting New Boohs. 469 



was evidently owing to the great scattering of the rays by the 

 substance. The india rubber being laid in contact with the 

 plate, and an exposure made through it, showed that it was 

 transparent to all rays from 10,000 to 5000. The absorp- 

 tion-spectrum therefore differed ; and it is evident that in 

 ebonite the india rubber is chemically changed in composition. 

 The conclusion to be drawn is, that ebonite, when of small 

 thickness, transmits to some extent the rays of lowrefrangibility, 



LXII. Notices respecting New Boohs, 

 Eine neue Form elektrischer Abstossung. {A new Kind of Electric 



Bepulsion.) By Dr. Eugen Goldstein. Berlin : Julius Springer. 



1880. 

 rPHE work before us is an octavo of nearly 200 pages, with six 

 -*- plates of lithographed figures, forming the first part of Dr. 

 Goldstein's ' Eesearches on the Electric Discharge in Gases.' It 

 contains minute and careful descriptions of experiments which 

 have occupied the author for eight years, and discussions of the 

 conclusions to which the experiments lead. The final conclusion 

 arrived at is, that the phenomena observed are not capable of expla- 

 nation in the present state of our knowledge — that they are not to 

 be explained by the known laws of electrostatic or of electrody- 

 namic repulsion, nor by the mutual mechanical action of molecules. 

 So far, therefore, the ground has been cleared by showing to what 

 the phenomena are not due ; and further investigations on this sub- 

 ject from the skilful hands of Dr. Goldstein will be looked for with 

 much interest. 



In the Introduction we are reminded of the appearance of the 

 electric discharge in an ordinary vacuum-tube (of simple cylindrical 

 form) filled with air or some other permanent gas. At atmospheric 

 pressure the discharge consists of a thin thread-like spark (the 

 " trait de feu ") and the surrounding glow or " aureole." As the 

 tube is gradually exhausted the " trait de feu " disappears first, and 

 the aureole remains and expands and fills the tube with light, in 

 which are usually distinguished two portions — the positive and ne- 

 gative "glows." From the positive pole or anode there proceeds a 

 stream of light expanding towards the opposite pole, which in air 

 is of a reddish colour, termed the positive discharge ; it shows, as 

 soon as the exhaustion has reached a certain point, regularly alter- 

 nating maxima and minima of light — the so-called stratifications. 

 The number of the stratifications varies not only with the density 

 and nature of the gas, but also with the width of the tube and the 

 distance between the electrodes. The positive light however, is, 

 not a necessary portion of the discharge ; and its presence or absence 

 depends on the ratio of the distance between the electrodes and the 

 smallest diameter of the tube at right angles to the line of discharge. 

 If this ratio is not greater than 2, then (at small densities) there is 

 no positive discharge. 



Erom the negative pole or kathode there proceeds also a luminous 

 discharge, which also consists of layers (or stratifications), whose 



