CONCEPTS OF PHYSICAL SCIENCE. 63 



prevalence among electricians to the fact that by virtue of long famil- 

 iarity we prefer to think in terms of matter, which is tangible, rather 

 than of ether. 



Charge is to be regarded as fundamental, and its substitute, quantity 

 of electricity, as merely an artificial term of convenience; because of 

 the former we have a definite mechanical conception, whereas we can 

 intelligently define a quantity of electricity only in terms of charge. 

 In the science of heat the case differs in that the term heat is used, 

 if not as precisely synonymous with energy, at least for a quantity 

 having the same dimensions as energy and having as its unit the erg. 

 It might easily have happened, as has happened in electrical theory, 

 that the ancient notion of a heat substance should survive, in which 

 case we should have had for the quantity of heat not something meas- 

 ured in terms of energy, but, as in the case of electricity, one of the 

 terms which enter into our expression for energy. We should then 

 have had to struggle continually, in thermo-dynamics, as we now do 

 in electrical theory, against the tendency to revert to an antiquated 

 and abandoned view. 



It would, I can not but think, have been fortunate had the word 

 electricity been used for what we now call electrical energy; using 

 charge, or some other convenient designation, for the quantity Q. 

 That aspect of the science in accordance with which we regard it as a 

 branch of energetics in which movements of the ether are primarily 

 involved would have been duly emphasized. We should have been 

 quit forever of the bad notion of electricity as a medium, just as we 

 are alreadv freed from the incubus of heat as a medium. We should 

 have had electricity — a mode of motion (or stress) of the ether as we 

 have heat — a mode of motion (of matter). When our friends asked 

 us : ' What is electricity ?' we should have had a ready answer for 

 them instead of a puzzled smile. 



One real advance which has been attained by means of the theory 

 of ionization, and it is of extreme significance and of far-reaching im- 

 portance, consists in the discovery that electrification or the possession 

 of charge, instead of being a casual or accidental property, temporarily 

 imparted by friction or other process, is a fundamental property of 

 matter. According to this newer conception of matter, the fruit of the 

 ionic theory, the ultimate parts of matter, are electrically charged par- 

 ticles. In the language of Eutherford:* 



It must then be supposed that the process of ionization in gases consists in 

 a removal of a negative corpuscle or electron from the molecule of gas. At at- 

 mospheric pressure this corpuscle immediately becomes the center of an aggrega- 

 tion of molecules which moves with it and is the negative ion. After removal of 

 the negative ion the molecule retains a positive charge and probably also becomes 

 the center of a cluster of new molecules. 



The electron or corpuscle is the body of smallest mass yet known to science. 



* Rutherford, ' Radioactivity,' p. 53, 1904. 



