Travers. — Presidential Address. 125 



from the power which the X rays afford of exploring the 

 human body, its chief importance for theoretical science lies 

 elsewhere. Unlike the electric waves of Hertz, they are not 

 capable of either refraction or polarization, and, although they 

 appear to have something in common with the invisible ultra- 

 violet rays of the spectrum, they differ from them in most 

 respects, and especially in their electric effects. It appears 

 that they do not emanate from the kathode itself, but originate 

 from the glass of the tube where it is struck by the kathode 

 rays, and, whilst these are capable of being deflected by the 

 magnet, the X rays take no notice of it, and pursue their course, 

 in spite of any interposed medium, in perfectly straight lines. 

 What, then, are these rays? For the present the ordinary en- 

 quirer must be content with the knowledge we have of their 

 power of piercing substances impervious to all ordinary rays of 

 light, and of recording a shadow upon a photographic film. 

 Whether or not the results of the experiments already made are 

 to be accepted as affording evidence that waves of compression 

 and rarefaction are produced in the so-called ether by the pas- 

 sage of light through it, must remain open until the learned phy- 

 sicists who are now engaged in investigating the structure and 

 movements of the ultimate particles of matter have had time 

 to deal with the application of this new discovery to the solu- 

 tion of the problems involved. Kontgen himself concludes the 

 paper referred to in these words : " Should not the new rays be 

 ascribed to longitudinal waves in the ether ? I must confess 

 that I have in the course of this research made myself more 

 and more familiar with this thought, and venture to put the 

 opinion forward, whilst I am quite conscious that the hypo- 

 thesis advanced still requires a more solid foundation."''' 



Discovery of Argok. 

 It might well have been thought impossible that any of the 

 constant elements of atmospheric air, which has so frequently 

 been analysed and examined by chemists and physicists in 

 the foremost rank of science, could long have escaped detec- 

 tion, but, singularly enough, it was not until last year that 

 the nitrogen of which it is so largely composed, amounting, in 

 effect, to nearly four-fiths of its volume, was conclusively proved 

 to be associated with an unknown chemical element. The com- 

 pound character of atmospheric nitrogen had, however, long 

 been suggested, and even to some extent demonstrated, by the 

 older chemists, for we find that Berzelius, a contemporary 



* Since this part of my address was written I have received the 

 April number of Nature, in which readers will find papers of the highest 

 interest by Professors J. J. Thomson and Oliver Lodge, on the subject of 

 the Rontgen rays, but the contents do not materially affect what I have 

 ventured to bring before the society. 



