THE X RAYS. 771 



putes to arbitration and England eight, and of these four were 

 between England and the United States." The writer, W. J. 

 Gennadius, quotes two very apposite declarations, one by General 

 Grant, and one by that experienced and sagacious statesman, the 

 late Earl Russell. Grant's words are, " Though I have been 

 trained as a soldier, and have participated in many battles, there 

 never was a time when, in my opinion, some way could not have 

 iDeen found to prevent the drawing of the sword." And Earl 

 Russell's : " On looking at the wars which have been carried on 

 during the last century, and examining into the causes of them, I 

 do not see one in which, if there had been proper temper between 

 the parties, the questions in dispute might not have been settled 

 without recourse to arms." These declarations are worth reflect- 

 ing on. The proviso introduced by Earl Russell is particularly 

 significant : " If there had been proper temper between the parties." 

 That is what is wanted, " proper temper." It resolves itself thus 

 into a question of national righteousness. The cynic may laugh 

 at the conclusion ; but those who are not cynics will venture to 

 believe that the problem is not hopeless. 



THE X RAYS. 



BY JOHN TKOWBRIDGE, 



RUMFORD PROFESSOR AND LECTURER ON THE APPLICATION OF SCIENCE TO THE USEFUL ARTS, 



HARVARD UNIVERSITY. 



SINCE the publication of Hertz's paper on the penetration of 

 thin sheets of metal, notably aluminum, by the cathode 

 rays, interest in the remarkable phenomena investigated first by 

 Prof. Crookes has been reawakened to a marked degree; and 

 most physicists during the past five years have regarded the sub- 

 ject of cathode rays as the most important one in electricity. In 

 1893 Lenard succeeded, by means of a Crookes tube provided 

 with a small aluminum window, in detecting the cathode rays 

 outside the tube in the air space of an ordinary room. He used 

 paper disks covered with a very fluorescent substance, which be- 

 came luminous when the cathode rays struck them ; and he also 

 succeeded in showing photographic effects of the rays. Now 

 Rontgen, by the use of ordinary dry plates and without the use 

 of an aluminum window, has taken photographs through wood 

 and through the human hand by means of what he terms the X 

 rays, which he supposes are excited either in the glass walls of 

 the Crookes tube or in the media outside the tube by means of 

 the cathode rays. 



We see, therefore, that the literature of the subject must be 



