350 POPULAR SCIENCE MONTHLY 



No more for an observer, carried along himself in a translation he 

 does not suspect, could any apparent velocity surpass that of light ; and 

 this would be then a contradiction, if we did not recall that this ob- 

 server would not use the same clocks as a fixed observer, but, indeed, 

 clocks marking ' local time.' 



Here we are then facing a question I content myself with stating. 

 If there is no longer any mass, what becomes of Newton's law? Mass 

 has two aspects: it is at the same time a coefficient of inertia and an 

 attracting mass entering as factor into Newtonian attraction. If the 

 coefficient of inertia is not constant, can the attracting mass be? That 

 is the question. 



Mayers Principle. — At least, the principle of the conservation of 

 energy yet remained to us, and this seemed more solid. Shall I recall 

 to you how it was in its turn thrown into discredit? This event has 

 made more noise than the preceding, and it is in all the memoirs. 

 From the first works of Becquerel, and, above all, when the Curies had 

 discovered radium, it was seen that every radioactive body was an inex- 

 haustible source of radiation. Its activity seemed to subsist without 

 alteration throughout the months and the years. This was in itself a 

 strain on the principles ; these radiations were in fact energy, and from 

 the same morsel of radium this issued and forever issued. But these 

 quantities of energy were too slight to be measured; at least that was 

 the belief and we were not much disquieted. 



The scene changed when Curie bethought himself to put radium 

 in a calorimeter ; it was then seen that the quantity of heat incessantly 

 created was very notable. 



The explanations proposed were numerous; but in such case we 

 can not say, ' store is no sore.' In so far as no one of them has pre- 

 vailed over the others, we can not be sure there is a good one among 

 them. Since some time, however, one of these explanations seems to 

 be getting the upper hand and we may reasonably hope that we hold 

 the key to the mystery. 



Sir W. Eamsay has striven to show that radium is in process of 

 transformation, that it contains a store of energy enormous but not 

 inexhaustible. The transformation of radium then would produce a 

 million times more heat than all known transformations ; radium would 

 wear itself out in 1,250 years ; this is quite short, and you see that we 

 are at least certain to have this point settled some hundreds of years 

 from now. While waiting, our doubts remain. 



