CHAP. XL] SCIENTIFIC WORK. 317 



A mass of correspondence, containing numerous 

 suggestions made by Maxwell from day to day in 

 1863-4, has been preserved by Professor Jenkin. Two 

 of the least technical passages will be found amongst 

 the letters in this chapter (pp. 337, 340). 



Another very important experimental investigation 

 conducted by Maxwell about this period was the 

 determination of the ratio of the electromagnetic and 

 electrostatic units of electricity, for the purpose of 

 comparing this quantity with the velocity of light. 

 As this investigation will be again referred to in Part 

 II., it is only necessary to say here that the experiment 

 amounts to a comparison between the attractions of two 

 electric currents flowing in coils of wire, and the attrac- 

 tion or repulsion between two metal plates which have 

 each received a charge of electricity. Maxwell had 

 pointed out that, in accordance with his theory, the 

 ratio of the units should be equal to the velocity of 

 light, and the value obtained by him was intermediate 

 between the extreme values obtained for that velocity 

 by previous observers. The experiment was the out- 

 come of his theory of the constitution of the space in 

 the neighbourhood of magnetic and electric currents, 

 by which he accounted for all the then known 

 phenomena of magnetism and electricity, and which 

 he published in a semi-popular form in the Philo- 

 sophical Magazine in. 1861 and 1862. 



During most of the King's College time Maxwell 

 resided at 8 Palace Gardens Terrace, Kensington, where 

 he carried on many of his experiments in a large garret 



