226 SCIENCE PROGRESS 



It had been stated in Part I. that Rutherford measured the 

 mass of the a-particle carrying unit charge of electricity ; it is 

 about twice that of hydrogen. He concluded that the a-particle 

 consisted either of a half-atom of helium, carrying one electric 

 charge, or a whole atom carrying a double charge. His recent 

 work shows that there is strong evidence for regarding the 

 latter assumption as established. In view of the large number 

 of radioactive substances emitting a-particles it is interesting to 

 note that the only cases in which the production of helium can 

 be regarded as proved are cases in which emanations are 

 present. In this connection its possible production from radio- 

 lead certainly demands careful re-investigation. 



The quantity of helium produced from radium bromide was 

 measured roughly by Ramsay and Soddy. It is of an order 

 which, when considered in connection with the total amount of 

 radio-active changes taking place, lends support to the sug- 

 gestion that all the helium in the earth's atmosphere has been 

 produced by such transformations. The questions must at 

 once arise : are these transformations limited to the production 

 of helium ? can no other gases of the argon series be produced 

 thus ? 



Section II. — Recent Attempts at Transmutation 



The alchemistic doctrine of transmutation was accepted by 

 most thinkers until the beginning of the sixteenth century. The 

 modern definition of an element is due to Boyle, and scarcely 

 can be said to have received wide acceptance by the end of that 

 century. His predecessors put forward some form or other of 

 the elements of the ancients, of which the Aristotelian system — 

 earth, air, fire, and water — is typical. Such elements were in 

 reality properties, which each substance possessed in different 

 degrees. With such conceptions a belief in transmutation 

 might easily arise, since if two substances consisted of different 

 proportions of these elements, they should be capable of trans- 

 formation into one another by altering the proportions. 



The belief in transmutation arose at a very early date ; 

 attempts to transmute base metals into gold or silver date to 

 the Egyptian era. (The name ^//.eta, given to this art, is possibly 

 derived from chemi, an old name for Egypt.) Superficial obser- 

 vations of a nature easy to comprehend led to these attempts. 

 Thus iron utensils left in copper mines were coated with a 



