396 JAMES CLERK MAXWELL. [CHAP. XII, 



scientific hypothesis they can get hold of. The Christian 

 Knowledge Society are publishing my charge. When it is 

 published I shall ask you to do me the favour to accept a 

 copy. You will then see that the best note in the little 

 volume is due to your kindness and aid. I remain, with 

 all good wishes, and sincere thanks, very faithfully yours, 

 C. J.- GLOUCESTER AND BRISTOL. 



(P.S.) If you are in London in the spring and near the 

 Athenaeum, do me the kindness of looking in on me, as I 

 shall be very glad to make -your personal acquaintance. I 

 am commonly in town regularly after Easter. 



To PROFESSOR LEWIS CAMPBELL. 



Glenlair, Dalbeattie, Christmas 1876. 



45. ... I hope that when this severe weather is past you 

 will be able to derive benefit from a moderate use of Plato 

 and Sophocles. 



We intended to have gone round by Edinburgh, to pay 

 Aunt Jane a visit ; but we both had such bad colds that we 

 came home to nurse them, and are now snowed up, and 

 enjoying the artificial heat of coals, peats, and sticks 

 judiciously intermingled. 



The demonstrator at the Cavendish Laboratory has been 

 out of sorts all this term, and has had to go home about a 

 month ago, so we have not been in full force there. I hope 

 he will be well in February, to absorb the energy of the new 

 B.A.'s set free from the Tripos and its attendant anxieties. 



As we get richer in apparatus, mathematical lectures 

 give way to experimental, and the black board to the lamp 

 and scale. I have had a pupil quite innocent of mathe- 

 matics who has learned to measure focal lengths of lenses, 

 and has found the electro-motive force from the water-pipes 

 to the gas-pipes, and from either set of pipes to the lightning- 

 conductor. 



I have been making a mechanical model of an induction 

 coil, in which the primary and secondary currents are repre- 

 sented by the motion of wheels, and in which I can symbolise 



