HELIUM ABBOT. 123 



cal elements. This is a property which it shares with some of the 

 other rare gases discovered about the same time — argon, neon, xenon, 

 and others. 



Readers will admit that up to this point the history of helium had 

 been one of surprises. Found originally in the sun, 90,000,000 miles 

 away; traced to the stars, thousands of times as far away as the sun; 

 over a quarter of a century elapsed before it was found upon the 

 earth, and when found, although a chemical element, it differed from 

 almost all chemical elements in being wholly indifferent to all other 

 constituents of the world. But the wonders of the story had hardly 

 begun. 



In 1898 the discovery of radium, another chemical element, sur- 

 prised the world, for the properties of radium were found more 

 strange than those of helium. Radium was found to be continually 

 giving off portions of itself. It was found to be capable of fogging 

 photographic plates through solid sheets of metal entirely opaque 

 to light. It was found to be continually giving up heat, and some 

 persons thought that here at last was a violation of the well-known 

 second law of thermodynamics, which maintains that heat can not 

 continually flow by a self-acting process from a cooler body to a 

 warmer one. This paradox was later understood, for it was found 

 that the shooting off of a part of itself by the radium made available 

 those stores of inner chemical energy which could be continually 

 converted into heat energy almost inexhaustibly in point of time. 

 With the discovery of this extraordinary property of radium the 

 mystery of the long existence of life upon the earth and the next 

 corollary to it, the long existence of the sun as a source of radiation, 

 became less puzzling. For although no sources of energy known up 

 to that time had been suggested which were competent to maintain 

 the sun's radiation for the hundreds of millions of years demanded 

 by the geologist and the zoologist to account for the phenomena they 

 study, yet if there be chemical elements which decompose their 

 inmost atoms with a continual evolution of heat, here may be an 

 almost unlimited source from which to draw for all demands of 

 geology and biology, as far as they relate to the sun. 



Rut what became of the particles shot off by radium ? They were 

 found to consist of gases, and some of these gases themselves were of 

 short life and eventually split up into others. Two stable products 

 of the decomposition of the atoms of radium and its immediate prod- 

 ucts were at length recognized. One of these is the well-known metal 

 lead, the other is our friend helium. Not only does radium break 

 up with the evolution of helium, but also uranium, thorium, and 

 possibly also other chemical elements. Thus was explained the 

 tendency of helium to be associated with uranium ores, for un- 



