62 DISCOVERY CH. 



solar prominences at any time when the sun is shining ; 

 and he then found that in addition to hydrogen, the 

 light of these tremendous flames commonly exhibited 

 in the spectroscope a line or ray which could not then 

 be matched with light from any terrestrial substance. 

 The enigmatical light appeared to be the exclusive 

 possession of bodies at the intense temperature of the 

 sun ; and for this reason Sir Norman Lockyer gave to 

 the substance emitting it the name helium the element 

 of the sun. It was not until twenty-six years later that 

 helium was isolated by Sir William Ramsay ; so that we 

 have the remarkable fact of an element being actually 

 discovered on the sun long before it was found on the 

 earth. 



Helium is now known to occur in many minerals, 

 and fairly large quantities of the gas are brought 

 annually to the earth's surface dissolved in the waters 

 of deep-seated mineral springs, like those at Bath, being 

 produced in all probability by the disintegration of that 

 wonderful element radium. The minute differences 

 between the weights of atmospheric and chemical 

 nitrogen observed by Lord Rayleigh in 1892 are thus 

 seen to be connected, link by link, with the marvellous 

 properties of radioactive minerals. 



The diligence and persistence shown by men of 

 science in the pursuit of knowledge are as remarkable 

 as acuteness of vision and quickness of understanding. 

 When Herschel was constructing the great mirror for 

 his telescope, he had to do all his polishing by hand, 

 and he found when once the final stage had begun, it 

 was necessary that it should never stop even for a 

 moment. His sister, Caroline, relates how she was 

 kept busy in attending on her brother when polishing : 

 " Since by way of keeping him alive I was constantly 



