MODERN VIEWS ON MATTER. 225 



and it was surmised that })<)ssil)ly the bari'iors bctwoen one species and 

 the next were not al)sohit(^ly infran_oihl(>, hut that temporary transi- 

 tional forms might occur. All this was sp(^culation; hut here in radio- 

 active matter the process appears to l)e going on l)et'ore our eyes. 

 Professor Rutherford and ^Tr. Soddy. who in Canada during the present 

 year have worked hard and admirably at the sul)ject, have adduced 

 .facts which point clearly in this direction; and thev initially describe 

 what appear to bo the tirst links of a chain of substances, all produced 

 in hopelessly minute (puintities reckoned by ordinary tests, but which 

 yet by electrical means can easily be detected, and their l)oiling points 

 and other properties investigated. Moreover, the investigators of 

 these strange substances are able to dissolve and precipitate, and per- 

 form ordinary chemical operations on, these utterly imponderable and 

 hopelessly mimite deposits of I'adio-active substances, 1)ecause of the 

 powerful means of detection which their ionizing power puts into our 

 hands — even a few stray atoms being able by their ionizing power to 

 discharge an electroscope appreciably. 



18. Thus, then, it would appear that our theoretical conclusion con- 

 cerning the inevitable radiation and loss of energy from electrically 

 constituted atoms of matter, a loss wdiich must involve them in neces- 

 sary change and dissolution, meets with quite unexpectedi}' rapid con- 

 firmation, and it is for that reason that I feel willing to accept tenta- 

 tively and as a working 'hypothesis this explanation of radio-activity. 

 It represents a fact previously wanted on theoretical grounds. For 

 how is radio-activity to be explained? It looks as if the massive and 

 extremely complex atoms of a radio-active suljstance were liable to get 

 into an unstable condition, probably reaching this condition whenever 

 any part of it attempts or is urged to move with the velocity of light. 

 I have showni elsewhere" that the mere fact of radiation will act as a 

 resisting medium and increase the speed of the particles automatically, 

 on the same principle that a comet would be accelerated if it met with 

 resistance, since the inverse-square law applies to electrical central 

 forces. Electrical mass is not strictly constant; it is a function of 

 speed, but in such a wa}' that it is practically^ constant until the velocity 

 of light is very nearly attained. That is a critical velocity, wdiich 

 apparently can not be surpassed. When this critical speed is reached 

 any electrilied bod}" becomes suddenly of infinite mass, and something 

 is boimd to happen. AVhat that something is, it is not easy theoret- 

 ically to say, but the partial or incipient disintegration or dissociation 

 of the atom and the flying away of a portion with a speed compara])le 

 to that of light is no unlikcdy result. 



Out of the whole multitude of atoms, even of the atoms of a con- 

 spicuously radio-active substance, it is prol)al>le that only a very few 

 get into this unstable or critical condition at any one time; perhaps not 



f'^ee. Nature, June 11, 190.3. 



