122 Transactions. — Miscellaneous. 



make no sensible impression upon the retina. It is more than 

 probable that in this we differ from many of the lower animals, 

 especially amongst those which roam by night ; but upon this 

 point I do not pretend to be in a position to offer more than 

 the suggestion. These ultra-violet rays, however, are those 

 which most stroogly, if not exclusively, affect the sensitive 

 photographic plate, and therefore photography by means of 

 that peculiar anomaly invisible light — viewing its effect from 

 the standpoint of human vision only — -is no new thing. What 

 is entirely new in the X rays, and the points in which they 

 differ completely from the Hertz electric waves (which, as 

 already shown, possess all the properties of, and are capable 

 of being reflected, broken, and polarised in the same way as, 

 ordinary light) are that they have an incomparably smaller 

 speed, are with difQculty reflected, are incapable of being re- 

 fracted or polarised, and otherwise differ in so many respects 

 from the latter as altogether to upset the cm-rent ideas about 

 light. It has, indeed, been suggested that they belong to the 

 borderland between light and electricity discovered by Hertz, 

 and only those who have watched the progress of the re- 

 searches made by experimenters following the suggestions of 

 Hertz, and especially those made by Professor Lenard, could 

 possibly have foreseen the existence of radiations having such 

 singular properties. 



Shortly before Hertz's death he noticed that, when the 

 streams of apparently luminous matter already alluded to 

 were projected against a thin plate of matter opaque to ordi- 

 nary light, the light produced appeared to pass through it. 

 For the purposes of his experiments in the same direction 

 Professor Lenard transferred the kathode rays from the tube 

 in which they were generated into another tube where he 

 could use them in a variety of ways. This transfer was 

 effected through a window composed of leaf aluminium, which 

 would have completely intercepted rays of ordinary light, but 

 through which the kathode rays passed at once into the next 

 tube, a strong smell of ozone being developed during their 

 passage. He afterwards found that a large proportion of the 

 rays which passed through the window were invisible, for 

 when the whole were thrown upon a paper screen covered 

 with fluorescent matter this matter began to glow precisely 

 as it would have done under an ordinary beam of sunlight 

 or of electric arc light ; but his experiments showed also that 

 in many other respects their behaviour was quite different 

 from that of ordinary light. To ascertain the nature of this 

 difference he passed theni through a variety of gases, liquids, 

 and solids, his operations being thus summarised by a writer 

 from whose work I have derived much assistance in preparing 

 this part of my address : — 



