34 PHYSICAL FORCE 



is the origin of the stream of energy pouring out into 

 space from stars so numerous that every living- person 

 in the world might claim a separate one as his own ? 

 That is the problem that has stared us in the face 

 since we began to understand the laws of energy, an 

 academic problem, perhaps, until it is realised that it 

 is necessary for us to be able to get our hands on the 

 levers controlling the primary sources of energy, or, 

 when our fuel supplies are exhausted, relapse into 

 barbarism. 



At the close of the nineteenth century an extra- 

 ordinary series of discoveries in physics and chemistry 

 put into our hands a scrap of a material called 

 radium, which asked us precisely the same question 

 as the stars, but at point-blank range. It is a new 

 element discovered by M. and Mme. Curie in 

 a uranium - containing mineral, pitchblende. It 

 possesses the outstanding property of emitting 

 energy, in relatively large amount, and in new and 

 surprising forms, spontaneously and continuously. 

 All we have learned of this new property, radio- 

 activity, shows that this steady emission of energy is 

 going on in the rocks, from which the radium is 

 extracted, at precisely the same rate as from the 

 radium after it has been extracted, and has been 

 going on for hundreds of millions of years. The 

 explanation follows from the discovery that these 

 radioactive elements are undergoing slow changes 

 into other elements, changes of precisely the same 

 kind as the alchemist sought to effect when he strove 

 in vain to transmute the base metals into gold. 

 Modern chemistry is unable to achieve such changes, 

 but they are now known to be going on slowly and 

 spontaneously in the radioactive elements. We can 

 at present only watch and follow them. * We have 

 not yet succeeded in interfering with them or 

 quickening their rate. 



