14 Prof. S. P. Thompson on the Conservation of Electricity, 



The experimental evidence which exists forbids us, more- 

 over, to think that the absolute quantity of electricity within 

 a closed surface can be altered by the transformation of any 

 other physical quantity into electricity. For, indeed, electri- 

 city belongs to a category by itself. It does not possess mass, 

 and therefore is not a form of ordinary matter ; it does not 

 conform to the same physical dimensions* as energy, and there- 

 fore cannot be in itself a form of energy. Neither matter nor 

 energy, then, can be transformed into electricity ; nor can 

 electricity be itself transformed into either of these physical 

 quantities. 



Therefore any system of electric bodies — that is to say, any 

 system whose parts consist of definite quantities of electricity — 

 must be regarded as a conservative system, and therefore sub- 

 ject, when regarded as a system, to a definite Law of Conser- 

 vation. 



2. These considerations have therefore led the present 

 writer to propound elsewhere f, in general language, a doc- 

 trine of the Conservation of Electricity similar to those already 

 recognized as holding good in the case of two other physical 

 entities — Matter and Energy. 



The author proposes in the present paper to trace out some 

 of the bearings of the doctrine of the Conservation of Elec- 

 tricity, particularly in relation to the questions of the Distri- 

 bution of Electricity in Space and of the Absolute Scale of 

 Electrification. 



3. Although the late Professor Clerk Maxwell used the 

 clear and emphatic language quoted above, the idea of the 

 ultimate Conservation of Electricity appears to have been 

 rejected by him, in consequence of the negative results which 

 attended his experimental attempt to discover whether an elec- 



* Matter lias dimensions [M], Energy [ML 2 T~ 2 ], and Electricity 

 [M^Lf T _1 J. The latter value is obtained from a consideration of the 

 Law of Coulomb, that QxQ-^L 2 = force =[MLT- 2 ] j whence 



Q=[(ML 3 T- 2 )£]. 

 But the dimensions of self-attractive matter may be similarly considered 

 by Newton's Law that -M . M-fL 2 = force =[MLT~ 2 ], whence 



M=[-L 3 T- 2 ]. 

 And if this value be put in place of M in the dimensions of Q above, we 

 get Q==[V — 1(L 3 T -2 )], a quantity whose dimensions differ only from 

 those of M in being prefixed by the imaginary quantity V — 1. This 

 seems to indicate an important relation. 



t See reference in ' Nature/ vol. xxiv. p. 78, to Preface of the author's 

 1 Elementary Lessons in Electricity and Magnetism/ and to the indepen- 

 dent enunciation of the same doctrine by M. GK Lippmann, in Compter 

 Rendus, t. xcii. p. 1049. 



