FUNDAMENTAL CONCEPTS OF PHYSICAL SCIENCE 25 



The only way in which the noun electricity enters, in any definite 

 and legitimate manner, into our electrical treatises is in the designa- 

 tion of Q in the equations 



Q =fldt, C = Q\E, W = QE, etc. 



Here we are in the habit whether by inheritance from the age 

 of the electric fluid, by reason of the hydrodynamic analogy, or as 

 a matter of convention or of convenience merely of calling Q the 

 quantity of electricity. 



Now Q is " charge " and its unit, the coulomb, is unit-charge. The 

 alternative expression, quantity of electricity, is a purely conventional 

 designation and without independent physical significance. It owes 

 its prevalence among electricians to the fact that by virtue of long 

 familiarity 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 con- 

 ception, 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 

 measured 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 thermodynamics, as we 

 now do in electrical theory, against the tendency to revert to an 

 antiquated and abandoned view. 



It would, I cannot 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 pri- 

 marily 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 already freed from the incubus of heat as a medium. We 

 should have had electricity a mode of motion (or stress), 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 

 importance, consists in the discovery that electrification, or the pos- 

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



