8o THE KINGDOM OF MAN 



pocket, it produces a destruction of the skin and flesh 

 over a small area in fact, a sore place. (2) The smallest 

 trace of radium brought into a room where a charged 

 electroscope is present, causes the discharge of the 

 electroscope. So powerful is this electrical action of 

 radium that a very sensitive electrometer can detect the 

 presence of a quantity of radium five hundred thousand 

 times more minute than that which can be detected by 

 the spectroscope (that is to say, by the spectroscopic 

 examination of a flame in which minute traces of radium 

 are present). (3) Radium actually realises one of the 

 properties of the hypothetical stone to which I compared 

 it giving out light and heat. For it does give out heat 

 which it makes itself incessantly and without appreciable 

 loss of substance or energy (' appreciable ' is here an im- 

 portant qualifying term). It is also faintly self-luminous. 

 Fairly sensitive thermometers show that a few granules 

 of radium salt have always a higher temperature than 

 that of surrounding bodies. Radium has been proved to 

 give out enough heat to melt rather more than its own 

 weight of ice every hour; enough heat in one hour to 

 raise its own weight of water from the freezing-point to 

 the boiling-point. After a year and six weeks a gram of 

 radium has emitted enough heat to raise the temperature 

 of a thousand kilograms of water one degree. And this 

 is alwa) T s going on. Even a small quantity of radium 

 diffused through the earth will suffice to keep up its 

 temperature against all loss by radiation ! If the sun 

 consists of a fraction of one per cent, of radium this 

 will account for and make good the heat that is annually 

 lost by it. 



This is a tremendous fact, upsetting all the calcula- 

 tions of physicists as to the duration in past and future 

 of the sun's heat and the temperature of the earth's 



