1-1 INAUGURAL ADDRESS. 



which are numerically accurate. But it has never been widely ac- 

 cepted. It requires not only the excessive penetration, but also a 

 velocity of radiation which is enormously greater than that of light, 

 for astronomical calculations show that the actions between the- 

 heavenly bodies do not take an appreciable time to cross the space 

 between them. Moreover, the energy of the radiation must reach 

 an appalling amount. It is interesting to observe, however, that the 

 penetration is no longer the difficulty that it used to be; and stiU more 

 interesting, perhaps, is the fact that the more penetrating the new 

 radiations are, the more nearly are their effects on different atoms 

 proportional to those of gravity. In the case of the most peneti'ating 

 gamma ray, the proportionality is almost exact, failing perhaps a 

 little for tlie heavier atoms. When we take less penetrating gamma 

 rays the effect is only exact in the case of the light atoms. If we were 

 to surround a number of small bodies with radium they would be 

 driven together by the gamma rays in such a way that every pair 

 would seem to exert an attraction on each other proportional to the 

 product of their masses, and inversely to the square of their distances 

 apart, which, of course, agrees with the law of gravitation. It cer- 

 tainly is very curious that we should actually be able to prove the 

 existence to a small amount, at least, of radiation which fulfils the 

 properties of Lesage's radiation on a small scale. It is useful in that 

 it illustrates the great difference between the new radiations and those 

 01 light and heat, and the closer resemljlance which they have to the 

 more fwndamental phenomenon of gravitation. But I need hardly say 

 that this is not enough to prove Lesage's theory. 



And, again, there is another problem in which the existence of a 

 veiy penetrating radiation has been considered as an aid to its solu- 

 tion. It is now generally held that the energy which is set free when 

 the various radiations are ejected from the radio-active atoms is 

 derived from a store internal to the atom. It is a most important 

 conception, for it is naturally extended to the case of all atoms, and 

 we have a glimpse of the existence of great quantities of energy exist- 

 ing within the atoms, and unutilised. Yet we have no warrant, as yet, 

 for the hope that we may some day succeed in unlocking these store- 

 houses. For, in the first place, the substances which liberate the 

 energ}'' of their own accord are few and rare, and other substances, 

 though they doubtless possess it, do not set it free. In the second 

 place, tlie action is beyond our control in the few cases in which we 

 know it to exist. 



A different view as to the origin of the energy was put forward by 

 several great physicists in the early days of the science-, notably by 



