150 ELECTRIC VIEW OF MATTER [CH. xv. 



that display of external activity which confers upon 

 the atom its observed properties. 



(5) A fifth view of the atom would regard it as a 

 central ' sun,' of extremely concentrated positive 

 electricity at the centre, with a multitude of electrons 

 revolving in astronomical orbits, like asteroids, within 

 its range of attraction. But this would give a law of 

 inverse square for the force, and consequently periodic 

 times dependent on distance, which appears not to 

 correspond with anything satisfactorily observed. 



All these views however are painfully indefinite, 

 except the third one, which regards positive electricity 

 as an indivisible unit of perfectly unresisting uniform 

 material (though ' material ' is not the right word), of 

 spherical form the size of an atom, in the midst 

 of which a definite geometrical arrangement of 

 electrons are revolving with known frequency in 

 specified groups or rings. The amount of outstanding 

 vagueness in this view is obvious ; and is necessary, so 

 long as we know little or nothing about the intrinsic 

 nature of what we experience as positive electricity ; 

 but at the same time all the rest of this hypothesis is 

 definite enough, and enables mechanical laws and 

 calculations to be applied with considerable fulness to 

 the elucidation of the phenomena that would be 

 displayed by such a ' model ' or hypothetical com- 

 bination. And if the so-calculated phenomena are 

 found to correspond with fact, it assuredly lends 

 some strength to the hypothetical basis on which the 

 calculation is founded; although it is certain to have 

 to be modified somewhat in the light of growing 

 experience as discovery proceeds. 



Whatever it may be worth, this is the only theory 

 of the nature of the atom which has been to any great 

 extent elaborated; and, extremely imperfect though it 



