GLOSSARY 291 



Then, crowning a long series of painstaking experi- 

 ments, Sir J. J. Thomson at the Cavendish Labora- 

 tory in Cambridge, discovered the negative electron, 

 and measured its mean statistical charge. The work 

 of Sir J. J. Thomson easily claims first attention. 

 There is, as Sir Arthur Schuster says, "no doubt 

 that Sir J. J. Thomson's experiment will be looked 

 upon in the future as a landmark in the advance of 

 science." Sir J. J. Thomson's epoch-making work in 

 1898 consisted in the experimental demonstration of 

 the existence of units of negative electricity, whose 

 mass is nearly 2,000 (1845) times smaller than the 

 mass of the hydrogen atom, the lightest atom known. 



And, finally, Robert Andrews Millikan in Ryerson 

 Laboratory, the University of Chicago, isolated the 

 electron and measured the unit electrical charge. 

 (1909.) Dr. Millikan determined the ionic charge, 

 compared it with the frictional charge; determined 

 the charge carried by a beta particle or the cathode 

 ray — all have the same value. (This value is stated 

 in the text, p. 119.) 



Energy, Physics. Whatever the form of the 

 energy, potential energy, kinetic energy, electric 

 energy, etc., energy always means "capacity for 

 performing mechanical work"; that is, the capacity 

 for accomplishing motion against the action of a 

 resisting force. According to Einstein's Theory of 

 Special Relativity, a quantity of energy represents a 

 mass; active energy represents momentum. The 

 mass is equal to the energy divided by c^. Einstein 

 says: "Mass and energy are therefore essentially 

 alike; they are only different expressions for the 

 same thing." See Quantum. 



Faraday's Law of Electrical Equivalence. In elec- 

 trolysis, the amount of a substance deposited by the 

 same quantity of electricity always is proportional 



