APR c.] DIMENSIONS 211 



opposite electricities were extracted from a milligramme of 

 water and given to two spheres one mile apart, those two 

 spheres would attract each other with a force equal to the 

 weight of 12 tons. 



APPENDIX D. 

 Dimensions of e/m Ratio. 



The reciprocal of the electrochemical equivalent of a 

 substance, e/m, may be expressed as regards dimensions in 

 several ways, one of which exhibits it as a certain large 

 numerical multiple of >v/(:y), the geometric mean between 

 Faraday's dielectric constant and Cavendish's gravitation 

 constant. For hydrogen, this numerical multiple is of 

 the order 10 18 ; for silver 10 16 . 



Another way is obtained by writing 



whence it follows that 



m/u.e 



centimetres\ 



-, / -, -. . //c 



and so em can be expressed in A /( - 



\ V grammes/ 



The artificiality of these dimensions is due to the fact 

 that e and m have been conventionally measured in 

 different ways ; m is measured by ratio of applied external 

 force to acceleration, while e, is measured by repulsive 

 force self-exerted on a similar charge at given distance. 



If we express //, as a density (see "Modern Views of 

 Electricity," Appendix p), the electrochemical equivalent 

 comes out as expressible in grammes per square centimetre, 

 that is to say a surface density. 



