IXAUGUKAL. ADDRESS. •>; 



we may a.-,cribe our power to isolate the negative. If we do so, w^e see 

 that it depends on certain relations between the speed mass and 

 electrical charge. The delta ray is the slowest moving negative 

 electi-on that can maintain an independent existence; it is scarcely set 

 free before its electrical forces attract it to some neighboui-ing atom to 

 which it becomes attached. The cathode rays have usually a far 

 higher speed, and can pass thz'ough many atoms without becoming 

 entangled therein. The beta rays of radium move faster still, and 

 can penetrate millions of atoms; in the open air they may move 

 llirough comparatively long distances without being deflected, perhaps 

 2 or 3 feet on the average. The speed of the delta ray is of the order 

 of a few hundred miles a second; that of the beta ray, 150,000 miles 

 a second. Now, if the mass of the negative electron were less, if it 

 were more easily turned aside, still higher speeds would be necessary 

 to preserve it from incorporation into the atom. It might be, there- 

 fore, that the positive electrons are lighter than the negative, and that 

 their separate existence requires a greater speed than can be given 

 them in siich a process of expulsion from the atom as occurs when a 

 delta ray is expelled, or can be communicated to them by artificial 

 means. We know that the positive electricity exists ; and exists in any 

 atom to an amount just sufficient to neutralise the negative charge. 

 It seems arbitraiy to assert that the positive cannot be subdivided to 

 as great an extent as the negative, and that we cannot conceive of so 

 small an amount of positive electricity as is sufficient to neutralise one 

 negative electron. It is convenient to make one other obsei'vation at 

 this stage. Just as the electron is known to be a constituent of all 

 atoms, yet is never obtained isolated, unless it is moving with suffi- 

 cient speed, so the electron together with enough positive to neutralise 

 it, the neutral pair or electrical doublet may be found in the atom, 

 and ma}^ exist separately under suitable conditions, e.g., when endowed 

 with suflicient speed, failing which it becomes incorporated. 



It will be seen, therefore, how scanty is our knowledge of the 

 positive constituent of the atom. When it is necessary to adopt some 

 hypothesis as a basis of calculation, it is only possible to choose one 

 which is simple, and, probably, therefore crude. Thomson presumes a 

 unifoi-m sphere of positive electricity in which the negative electrons 

 move freely ; through which it must also be supposed that other similar 

 spheres are able to pass, since, for example, the alpha particle 

 traverses atoms of all substances, and the alpha particle is an atom of 

 helium. 



To sum up, we may take as the third lesson that there is a 

 certain sameness in the materials of construction of the atoms; and 



