82 SCIENCE PROGRESS 



causes — firstly, to the ease with which it is absorbed by nearly 

 all substances ; secondly, to the circumstance that being of 

 higher refrangibility a larger proportion of its energy is avail- 

 able for the performance of work. 



In 1894 Ph. Lenard 1 showed that cathode rays which had 

 penetrated an aluminium window in a vacuum tube produced 

 ozone in the air through which they passed. Whether the 

 formation of ozone was due directly to the cathode rays or 

 indirectly to the ultraviolet light produced by the passage of 

 the cathode rays through air is doubtful. Lenard was unable 

 to detect any other chemical changes induced by the action of 

 this form of energy ; electrolytic gas did not explode, carbon 

 disulphide did not burn, hydrogen sulphide was unchanged 

 and nitrogen and hydrogen did not interact when subjected to 

 the rays. 



Lenard 2 also investigated somewhat exhaustively the effects 

 of ultraviolet light on gases. He showed, firstly, that under 

 the influence of light gases became conducting ; secondly, that 

 condensation nuclei were produced ; thirdly, that in the case 

 of oxygen ozone was formed. These effects were brought about 

 in air by light of wave-length 0*00014 to 0*00019 mm., that is, only 

 by the rays of highest refrangibility to which air is compara- 

 tively opaque. Hydrogen was more transparent to ultraviolet 

 light than air and accordingly was unaffected by light of greater 

 wave-length than o'oooi6 mm. To the most chemically active 

 rays, air at atmospheric pressure was more opaque than rock- 

 salt, fluorspar or quartz. It is important that this relative 

 opacity of air should be borne in mind in the construction of any 

 apparatus to be used in the examination of the chemical effects 

 of rays and that air spaces in the path of the rays should be 

 avoided. 



Closely connected with the above-mentioned work of Lenard 

 is an interesting research by E. Warburg, 3 in which the dis- 

 charge of electricity through oxygen from a point was investi- 

 gated. Under different conditions the amount of ozone pro- 

 duced was from 1,000 to 93 times greater than the amount 

 which would have been found had its production been due 

 entirely to electrolysis. From this fact the necessary con- 



1 Ann. Physik. 1894, 51, 225. 



2 Ibid. 1900, 70, 486. 



3 Sitzungsber. K. Akad. Wiss. Berlin, 1903, 1011. 



