334 Proceedings of the Royal Society 
to those who possess peculiarly ready mastery over symbols, whether 
they try to understand the significance of each step or no, Maxwell 
was not, and certainly never attempted to he, in the foremost rank 
of mathematicians. He was slow in “ writing out,” and avoided as 
far as he could the intricacies of analysis. He preferred always to 
have before him a geometrical or physical representation of the pro- 
blem in which he was engaged, and to take all his steps with the 
aid of this : afterwards, when necessary, translating them into 
symbols. In the comparative paucity of symbols in many of his 
great papers, and in the way in which, when wanted, they seem to 
grow full-blown from pages of ordinary text, his writings resemble 
much those of Sir William Thomson, which in early life he had with 
great wisdom chosen as a model. 
There can be no doubt that in this habit, of constructing a mental 
representation of every problem, lay one of the chief secrets of his 
wonderful success as an investigator. To this were added an extra- 
ordinary power of penetration, and an altogether unusual amount of 
patient determination. The clearness of his mental vision was quite 
on a par with that of Faraday; and in this (the true) sense of the 
word he was a mathematician of the highest order. 
But the rapidity of his thinking, which he could not control, was 
such as to destroy, except for the very highest class of students, the 
value of his lectures. His books and his written addresses (always 
gone over twice in MS.) are models of clear and precise exposition; 
but his extempore lectures exhibited, in a manner most aggravating 
to the listener, the extraordinary fertility of his imagination. 
During his undergraduateship in Cambridge he developed the 
germs of his future great work on “Electricity and Magnetism” 
(1873) in the form of a paper “On Faraday's Lines of Force,” which 
was ultimately printed in 1856 in the “Trans, of the Cam. Phil. 
Soc.” He showed me the MS. of the greater part of it in 1853. It 
is a paper of great interest in itself, but extremely important as 
indicating the first steps to such a splendid result. His idea of a 
fluid, incompressible and without mass, but subject to a species of 
friction in space, was confessedly adopted from the analogy pointed 
out by Thomson in 1843 between the steady flow of heat and the 
phenomena of statical electricity. 
In recent years he came to the conclusion that all such analogies, 
