1892.] On the Thermal Conductivities of Crystals, 



421 



round in each of the guns, using the driving rings marked A, B, and 

 C. As it would be useless to attempt to draw general conclusions 

 from single rounds, and as in guns of the calibre experimented with 

 the difference between the driving rings is not very marked, I have 

 treated the series as if all the rounds had been fired with the same 

 driving ring ; the results are given in Table IX. 



Table IX. Results of Experiments with Cordite. 



From the cordite experiments, it follows that the loss of energy due 

 to the uniform rifling is 21 ft.-tons, or 1'43 per cent., and to the para- 

 bolic rifling 34 ft.-tons, or 2'3 per cent. : the coefficient of friction 

 deduced from the loss of energy with the uniform rifling being 0'199, 

 or nearly the same value as was given in Table VIII. 



III. " On the Thermal Conductivities of Crystals and other Bad 

 Conductors." By CHARLES H. LEES, M.Sc., late Bishop 

 Berkeley Fellow at the Owens College, Manchester. 

 Communicated by Professor ARTHUR SCHUSTER, F.R.S. 

 Received January 22, 1892. 



(Abstract.) 



The author commences by pointing out the great differences be- 

 tween the results obtained in 1879 by G. Forbes for the con- 

 ductivities of quartz in different directions and those obtained in 

 1883 by Tuschmidt. He then refers to Kundt's discovery, that 

 the metals stand in the same order as conductors, and as to the 

 velocity of propagation of light through them, and mentions that his 



