THE ATOM 97 



"activated," that is, changes its orbit, or goes from 

 one energy-level to another. This important pro- 

 position has been experimentally verified. Thus 

 Karl Taylor Compton and his collaborators at the 

 Palmer Physical Laboratory (Princeton) found that 

 "the activated states of hydrogen are exactly as 

 he [Bohr] predicted them." "It was similarly 

 found," Dr. Compton said, "that the light of every 

 particular wave-length requires a definite amount 

 of energy for its emission and this energy is the 

 energy of a corresponding activated state of the 

 atom." {See Quantum.) 



The entire field of exploration of the atom through 

 spectrum analysis has been opened up — from the 

 series of the infra-red (Paschen) to the extreme 

 ultra-voilet (Lyman, Millikan, Bowen, and others) 

 and X-rays {see X-rays). 



It is, of course, well recognized, and there could 

 be no confusion concerning this fact — at least not 

 in the mind of a physicist — that the Bohr theory of 

 the atom accepts the nucleus of the atom and builds 

 around it in accordance with the evidence of spec- 

 tra and of the properties of the elements. ^^ 



The exact number of positive and negative elec- 

 trons contained in the nuclei of the atoms is believed 



1* As already noted, the "nucleus" atom theory was first advanced by Ruther- 

 ford. In connection with an impenetrable nucleus, however, Lenard's work, too, 

 may not be forgotten. 



