CHAPTER XI 



RADIO-ACTIVITY 



THE ATOM IN DISSOLUTION 



" From harmony, from heavenly harmony 



This universal frame began ; 

 When nature underneath a heap 



Of jarring atoms lay." DRYDEN. 



THE various manifestations of energy already dealt with have 

 all been associated with matter in the form of small aggregates 

 (colloids), atoms, or ions (charged hydrated atoms). Chemists 

 once defined the atom as the smallest non-divisible portion of 

 matter. Needless to say, many scientists were content to be 

 decryed as old fashioned and refused to accept this opinion of 

 the atom. My old teacher, Prof. John Ferguson, would allow no 

 one to refer to atoms. He preferred the more cumbrous but 

 exact term ' Combining Proportions." Modern work has con- 

 firmed these opinions of the atom. Physicists are now interested 

 in the structure of the atom. No longer is it considered as non- 

 divisible. No longer does it remain as fundamental. Of what 

 then does the atom consist ? Many and varied are the present- 

 day theories of its structure, but in general most schemes are 

 similar. It is supposed to consist of a number of smaller units, 

 negative electrons, all moving rapidly and irregularly round a 

 central positive charge. A negative electron is nothing more 

 than a unit charge of electricity. The number of electrons in 

 each ring is definite and may undergo alteration in definite 

 quanta only. 



(1) Not more than a certain number of electrons can continue 

 in stable motion in one ring. If more are added the system breaks 

 up into two or more rings. 



(2) If the orbital velocity of the rings exceeds or falls below a 

 certain critical value, the electrons are rearranged to ensure 



stability for that speed. 



117 



