4g A. W. Steivart on 



certainly, a mass seventeen hundred times smaller than a hydrogen 

 atom, and that they are really corpuscles of negative electricity 

 which we call electrons. 



But another set of iihenomena has been observed in the 

 Crookes' tul)e. 



If the cathode be pierced with a series of apertures, a second 

 set of rays " makes its appearance, travelling in the direction 

 opposite to that of the cathode rays. These are shown to be 

 streams of the molecules of the gas in the tube, each carrying one 

 or more positive charges, being named for this reason " Positive 

 Rays." In the dark they can be seen as faint pencils of light 

 traversing the tube. 



There is still a third type of " ray " observable, the X-rays. 

 These are rays of light of extremely short, wave length, related 

 to ordinary light as a note in the treble of a piano is to a note in 

 the bass. They are produced by the impact of electrons upon 

 matter, and in the Crookes' tube they originate where the 

 cathode rays strike the glass of the tube. They have the power 

 of making the air through which they pass a good conductor of 

 electricity. 



Both Dr. R. Beattie and Dr. P. T. Crymble, of the Queen's 

 University, have made valuable contributions to our knowledge 

 in this sphere, the one in pure Physics, the other in the applica 

 tion to medical and surgical problems. 



In 1896, the French scientist, Becquerel, was struck by the 

 resemblance of the green fluoresence of Crookes' tubes to the 

 lluoresence of certain salts of uranium, and it occurred to him 

 that these salts might be emitting X-rays. We know now that 

 his analogy was erroneous ; but when he tested these salts by the 

 photographic method, he found that there actually was an 

 emission of X-rays. This discovery by Becquerel opened up an 

 entirely new field of research, lying within the borders of both 

 Chemistry and Physics ; and at once there was a rapid extension 

 of our knowledge. Other elements, such as thorium, were found 

 to be radio-active, this being easily demonstrated by laying a 



