~ 
368 Thirty-first Meeting of the British Association. 
of important experiments were instituted by Mr. Hopkins, in the prose- 
cution of which Dr. Joule and myself took part; and after a long and 
laborious investigation it was found that the temperature of fluidity in- 
creased about one degree Fahrenheit for every five hundred pounds of 
pressure in the case of spermaceti, beeswax, and other similar substances 
to lead to the conclusion that the thickness of the earth’s crust is much 
Ww 
trine of central heat, but shows that only a part of the increase of tem- 
perature observed in mines and deep wells is due to the outward flow of 
that heat.” * * * 
“ Two other branches of scientific research, Geography and Ethnology, 
have for some years been united, in this Association, in one Section, and 
e 
displayed by our travellers in all parts of the world have been powerfully 
a 
the prominence and rapid publicity given to discoveries by th body 
have largely promoted geographical research. In Physical Geography, 
the late Baron von Humboldt has been one of the largest contributors, 
and we are chiefly indebted to his personal researches and nu oe 
Humboldt we owe our knowledge of the physical features of Central and 
Southern America. To Parry, Sir James Ross and Scoresby we are se 
bes! 
its tributaries, To thgse, we may add the explorations of Capt. Burtot 
in the same continent, and those also by Capt. Speke and Capt. Grant of 
