164 Dr. J. A. Fleming [May 30, 



and, in consequence of the electric charge it carries, it is virtually an 

 electric current, and can be deflected by a magnet. The proof which 

 has been given by Professor Thomson that this 'radiant matter' 

 consists of corpuscles, a thousand times smaller than an atom of 

 hydrogen in mass, and that they are shot off from the kathode with a 

 velocity which is comparable with that of light, explains at once 

 both their kinetic energy and also the manner in which they are 

 able to pass through windows of aluminium, as shown by Lenard, 

 and get into the space outside the tube. Furthermore, evidence has 

 been put forward to show that the electric charge carried by each 

 one of these tiny corpuscles is exactly the same as that which a 

 hydrogen atom carries in the act of electrolysis or when it forms a 

 hydrogen ion. 



It seems tolerably clear from all the facts of electrolysis that 

 electricity can only pass through a conducting liquid or electrolyte 

 by being carried on atoms or groups of atoms which are called ions — 

 i.e. wanderers. The quantity thus carried by a hydrogen atom or 

 other monad element, such as sodium, silver or potassium, is a definite 

 natural unit of electricity. The quantity carried by any other atom 

 or group of atoms acting as an ion is always an exact integer multiple 

 of this natural unit. This small indivisible quantity of electricity 

 has been called by Dr. Johnstone Stoney an electron or atom of elec- 

 tricity. The artificial or conventional unit of electric quantity on the 

 centimetre-gramme-second system, as defined by the British Associa- 

 tion Committee on Electrical Units, is as follows : 



An electrostatic unit of electric quantity is the charge which when 

 placed upon a very small sphere repels another similarly charged 

 sphere, the centres being one centimetre apart, with a mechanical 

 force of one dyne. The dyne is a mechanical unit of force, and is 

 that force which acting for one second on a mass of one gramme gives 

 it a velocity of one centimetre per second. Hence, by the law of 

 inverse squares the force in dynes exerted by two equal charges Q at 

 a distance D is equal to Q'/D-. Two other units of electric quantity 

 are in use. The electromagnetic unit, which is thirty thousand million 

 times as great as the electrostatic unit, and the practical unit called 

 the coulomb or ampere-second, which is three thousand million times 

 the electrostatic unit. We can calculate easily the relation between 

 the electron and the coulomb ; that is, between Nature s unit of elec- 

 tricity and the British Association unit, as follows : 



If we electrolyse any electrolyte, say acidified water which yields 

 up hydrogen at the negative electrode, we find that to evolve one 

 cubic centimetre of hydrogen gas at 0° C. and 760 mm. we have to 

 pass through the electrolyte a quantity of electricity equal to 8*62 

 coulombs. For 96,540 coulombs are required to evolve one gramme 

 of hydrogen and 11,200 cubic centimetres at 0° C. and atmospheric 

 pressure weigh one gramme. The number 8*62 is the quotient of 

 96,540 by 11,200. 



Various arguments, some derived from the kinetic theory of gases, 



