14 PRESIDElN^rS ADDRESS. 



finally been distinguisheil three classes o£ rays given off by radium : 

 (1) the alpha rays, which are only slightly bent, and ha\e little penetrative 

 power ; (2) the beta rays, easily bent in a direction opposite to that in 

 which the alpha rays bend, and of considerable penetrative power ; (3) the 

 gamma i-ays, which are absolutely unbendable by the strongest magnetic 

 force, and have an extraordinary penetrative power, producing a piioto- 

 graphic effect through a foot thickness of solid iron. 



The alpha rays ai'e shown to be streams of tiny bodies positively 

 electrified, such as are given off by gas flames and red-hot metals. The 

 particles have about twice the mass of a hydrogen atom, and they fly off 

 with a velocity of 20,000 miles a second ; that is, 40,000 times greater than 

 that of a rifle bullet. The heat produced by radium is ascribed to the 

 impact of these particles of the alpha ray.s. 



The beia i-ays are streams of corpuscles similar to those given ofi" 

 by the cathode in a vacuum tube. They are charged with negative 

 electricity and travel at the velocity of 100,000 miles a .second. They 

 are far more minute than the alpha particles. Their mass is equal to the 

 one-thousandth of a hydrogen atom. They produce the major part of 

 the photographic and phosphorescent effects of the radium rays. 



The (jamma rays are apparently the same, or nearly the same, thing 

 as the X-rays of B-ontgen. They are probably not particles at all, but 

 pulses or waves in the ether set up during the ejection of the corpuscles 

 which constitute the beta rays. They produce the same effects in a much 

 smaller degree as do the beta rays, but are more penetrating. 



The kind of conceptions to which these and like discoveries have led 

 the modern physicist in regard to the character of that supposed un- 

 breakable body —the chemical atom — the simple and unaffected friend of 

 our youth — are truly astounding. But I would have you notice that they 

 are not destructive of our previous conceptions, but rather elaborations 

 and developments of the simpler views, introducing the notion of struc- 

 ture and mechanism, agitated and whirling with tremendous force, into 

 what wc formerly conceived of as homogeneous or simply built-up 

 particles, the earlier conception being not so much a positive assertion of 

 simplicity as a non- committal expectant formula awaiting the progress of 

 knowledge and the revelations which are now in our hands. 



As I have already said, the attempt to show in detail how the marvel- 

 lous properties of radium and radio-activity in general are thus capable of 

 a pictorial or structural representation is beyond the limits both of my 

 powers and the time allowed me ; but the fact that such speculations 

 furnish a scheme into which the observed phenomena can be fitted is 

 what we may take on the authority of the physicists and chemists of our 

 day. 



Intimately connected with all the work which has been done in the 

 past twenty-five years in the nature and possible transformations of 

 atoms is the great series of investigations and speculations on astral 

 chemistry and the development of the chemical elements which we owe to 

 tlie unremitting labour during this period of Sir Norman Lockyer. 



