On the Specific Heat of Basalt. 353 



after a finality of knowledge lias been responsible for nume- 

 rous fruitless speculations in the past, and it seems only too 

 probable that the impatience of the mind with its own igno- 

 rance is the principal foundation of much of the theory of 

 to-day. The satisfaction derived from the contemplation of 

 simple and comprehensive laws may suffice perhaps to prove 

 that the powers of the mind are limited, but hardly that the 

 processes of nature are simple. 



XLIV. On the Specific Heat of Basalt. By W. C. Roberts- 

 Austen, C.B., F.R.S., and A. W. Rucker, F.R.S.* 



HAVING been asked by the Rev. 0. Fisher to determine 

 for him the latent heat of basalt, we made some ex- 

 periments on a specimen which was furnished to us by Prof. 

 Judd. 



Fragments of the rock were melted in a platinum crucible, 

 and the junction of a thermal couple consisting of platinum wiih 

 platinum containing 10 per cent, of rhodium was immersed 

 in the pasty mass, which was then allowed to cool. The scale 

 of the galvanometer had previously been standardized by an 

 observation on the solidifying-point of pure gold, and the 

 pyrometer was standardized from time to time by the same 

 means. When the index spot of light reached the desired 

 point the wires were nipped off close to the basalt, and the 

 crucible and its contents were plunged into 1000 grams of 

 water contained in a silver calorimeter. The water was 

 stirred by a screw or fan of silver which was rotated by an 

 electric motor. The temperature was read by means of a 

 mercurial thermometer which had been carefully corrected. 



The two main sources of error in the experiments are pro- 

 bably an uncertainty as to the mean temperature of the 

 basaltic mass owing to its being a bad conductor of heat, 

 and the fact that in the processes of heating and cooling it 

 undergoes more or less important changes of constitution. 



The first error was reduced to small proportions by using 

 small quantities of basalt, the mass employed rarely much 

 exceeding 20 grams. 



The second error is in part unavoidable. The rapidly 

 cooled basalt was always glassy like olivine. We also found 

 that frequent heatings and coolings, and the nature of the' 

 flame — whether oxidizing or reducing — employed to heat the 

 mass appeared to affect the results very seriously. 



In some experiments the crucible was heated in the flame 



* Communicated by the Authors. 

 Phil. Mag. 8. 5. Vol. 32. No. 197. Oct. 1891. 2 B 



