RADIOACTIVITY, 121 



than a gram in all. When Ave consider also that radium constantly 

 produces heat, the question is forced upon us whether this store of 

 heat has not already played an important part in the constitution 

 of the earth, and whether it may not now do so. Indeed, we may 

 ask the still more astonishing question, whether heat production by 

 the means of radium may not be considered in connection with the 

 heat of the sun on which all life on our globe depends. 



If we combine the Kant -Laplace hypothesis of the origin of our sun 

 system with the princij^le of energy, we reach the conclusion, as 

 Helmholtz has shown, that the existing supply of heat in the sun may 

 have arisen from the process of contraction, through which it was 

 formed in the beginning out of chaotic masses of nebula% and that 

 the continued radiation of heat by the sun is caused by the now 

 slower but still progressive contraction of the sun's mass. It is evi- 

 dent that if the existent amount of radium produces such enormous 

 quantities of heat, we must suppose the process of contraction to have 

 proceeded correspondingly slower, and we may therefore assume a 

 much longer existence than heretofore supposed, in the past as well 

 as in the future, for both the sun and the earth, a conclusion which 

 agrees with the vast periods of geologic development established by 

 quite different facts and researches. Still this and similar questions 

 to which the discovery of radioactivity has given rise must remain in 

 abeyance so long as the chief problem, whence does radium derive 

 its emitted energy, remains unsolved. We have asserted that a crys- 

 tal of it constantly emits a, ^, and y rays, can diffuse noticeable quan- 

 tities of heat and, tested by the most exact measuring instruments, 

 still remain the same. How can this be reconciled with the law of 

 the conservation of energy, which we know all the processes of nature 

 obey ? " The universe," says Helmholtz, ** has its limited supply 

 of energy, which works in it under ever-varying forms, indestruc- 

 tible, incapable of increase, eternal, and unchangeable like matter." 

 We define physics as the science which treats of the transformation 

 of energ}^ while conserving the quantity. We distinguish between 

 mechanical, chemical, and electrical energy, the energy of sound, of 

 light, of heat, and we assert that all physical processes in nature con- 

 sist only in the change of one kind of energy into the equivalent 

 quantity of another. No energy can be lost, and none can be created. 

 When we see, therefore, that radium is continually giving out energy, 

 and this fact is absolutely proved by manifold experiments, we are 

 compelled to ask. Whence comes this energy and from what is it 

 derived ? 



None of the processes of nature hitherto known to us can give the 

 answer, and we are confronted by a perplexing alternative: The 

 principle of energy, which we have hitherto held to be the highest 

 guiding law of the natural sciences, is false, or there are natural 



