14 PRESIDENTIAL ADDRESS. — SECTION I. 



this luminosity being caused by the bombardment ot the glass by 

 the ultra-gaseous particles of Crookes, or, as we now call them, 

 the corpuscles. Now it does not matter what is the nature of the 

 gas originally present in the tube, nor does the nature of the 

 electrode interfere ; the character of the corpuscle seems to remain 

 the same in all cases. Are these corpuscles material bodies, or 

 are they merely " waves " set up in the ether, as was at one time 

 thought ? The answer must be, I think, that they are material 

 bodies. Let us now study their specific properties. In the first 

 place they are travelling with tremendous velocity, and they move 

 in straight lines as we should expect material bodies to do. In 

 the second place, their direction of motion can be changed by the 

 action of a force, and in the third, they carry an electric charge, 

 which indicates that they must be composed of matter or some- 

 thing akin to matter. Against this view might be adduced the 

 difficulty of conceiving that such an enormous number of particles 

 could be shot off from any piece of matter, without its being 

 changed in weight, or altered in character, and also the fact that 

 the particles can pass through a piece of solid material. This 

 argument would have had considerable force before the discovery 

 of radium, but now we know that actual particles of matter may 

 be shot off continuously from radium for many years without 

 the original matter suffering a weighable loss of material. I have 

 in my possession several spinthariscopes, which have been under 

 observation for five years without their activity being appreciably 

 lessened — and to give a quantitative example, I hold in my hand 

 a piece of glass, on which was placed five years ago 11.700017 

 part of a grain of radium, and io-day sufficient radium remains to 

 indicate its presence. It will still excite luminosity in a dark room 

 — that is, it is still shooting off particles so numerous that they 

 cannot be counted. 



All the corpuscles shot off from the cathode are charged with 

 negative electricity, and this fact it is which enables us to find c^t 

 what the mass of the corpuscle is. So far we have not been able 

 to determine their mass directly, but as they are charged with 

 electricity we can in several ways obtain a value for the ratio of 



the charge to the mass of the corpuscle, that is, the famous 



m 



can be detex"mined in many ways, and the surprising result is seen 



that this ratio is practically the same, whether the corpuscles are 



obtained from the discharge of electricity in a vacuum tube or from 



those emitted by a hot wire, or by those thrown off from hot lime, 



or again by those produced by radio-active substances, such as 



uranium, radium, etc. In fact, these corpuscles are so universal 



and so associated with the most diverse kinds of matter — I think 



I may say with all kinds of matter — that one is led to believe that 



they are synonomous with matter itself. This piece of nickel is 



giving off at the present time none or, at most, very few corpuscles, 



but heat it to about 380° and they are given off rapidly. If 



corpuscles of the same character are thrown off from the most 



diverse kinds of matter, should it not be possible to conceive of the 



corj)uscles uniting to produce any kind of matter. To quote Sir 



