124 THE NEW KNOWLEDGE. 



years after its discovery on the sun it was identified by Sir 

 William Ramsay as a constituent of certain minerals in the 

 earth's surface. Its discovery both in the sun and in the 

 earth depends upon the fact that the element has a peculiar 

 characteristic spectrum (Fig. 40). It turned out to belong 

 to the Argon series of elements, those elements which 

 the reader will find tabulated in the zero group of the 

 periodic law (page 28), and which are all alike in the fact 

 that they are gases incapable of entering into chemical com- 

 bination and in this respect are different from all other ele- 

 ments. It is a very remarkable fact that this gas, helium, as 

 found on earth is always associated with radio-active min- 

 erals; and it soon occurred to many minds that possibly it 

 was a product of the atomic disintegration of the radium. 

 A few months ago this was the merest speculation but now, 

 thanks to the rapid progress of science, it looks as though it 

 were a veritable. fact. The discovery arose in the following 

 way : Sir William Ramsay and Mr. Soddy in the summer of 

 1903, were examining with the spectroscope the air which 

 had been bubbled through a solution of radium bromide in 

 order to find whether or not it was possible to discover any 

 traces of a spectrum of the emanation, which, the reader 

 will remember, is obtained in that way. They did discover 

 some bright lines which they ascribed to the emanation, but 

 after standing for some time the spectrum of helium made 

 its appearance and increased in brightness for several days. 

 This indicates that the helium is produced from the ema- 

 nation; that is to say that helium is a disintegration prod- 

 uct of the radium emanation. It is possible that the 

 helium consists of the alpha-rays or positively electrified 

 particles given out by the emanation. The fact that the 

 mass of the alpha particle is about twice that of the hydro- 

 gen atom bears out that idea, for the helium atom is next 



