between, the Granite and Slate in the Cornish Mines. 199 



likely to approach the true temperature of the earth at, and 

 near the place of observation, than if inserted in holes 

 bored in the sides of the galleries, or in rubbish long un- 

 moved, as both these are unquestionably much affected by 

 the air circulating in the vicinity, vehich, also, being itself 

 exposed to so many disturbing causes, cannot be regarded 

 as giving more than a very distant approximation to the 

 real temperature of a given spot. 



Confirmatory of the prevailing opinion of an increase of 

 temperature in descending — the foUovring observations 

 refer to the water as running or jetting out of the unbroken 

 rock at the " adit level," and of that pumped to the same 

 gallery from the deepest part of the mines. 



Granite. 



DpntTi Number of 



^^y^"' Observations. Temperatares. 



From Rock in adit 22-5 fathoms, 6 50^*4 



Pumped to adit from 110-0 fathoms, ..... 12 57°*2 



Slate. 



Denth Number of 



^ ' Observations- Temperatures. 



From Rock in adit 27-0 fathoms, 4 53° *4 



Pumped to adit from 113-0 fathoms, 17 60°'0 



These observations are also confirmatory of the diff*erence 

 between the temperatures of the granite and slate. 

 I have the honour to remain, 

 Sir, 

 Your very faithful, humble Servant, 



W. J. Henwood. 



1, Merrab Place, Penzance, 

 4th August, 1836. 



Article VII. 

 The Art of Dyeing. 

 {Continued from page 64.) 



BLUEISH GRAY, FROM COCHINEAL AND IRON MORDANT. 



The production of a darker shade is combined vrith many 

 difficulties, as iron mordants which contain the iron in the 

 state of peroxide form with the colouring matter of the 



