434 JOURNAL OF THE PLYMOUTH INSTITUTION. 
His family being more largely interested in the mines of Corn- 
wall than any other at that time, minerals, with their composition, 
crystallization, and their deposition in veins, naturally engaged his 
attention. In 1815 he and his friend Mr. Joel Lean requested 
Captain Thomas Lean to ascertain the temperature in the bottom 
of Crenver mine; he also furnished Captain Rule with thermometers 
to make similar observations in Dolcoath. The “ Transactions”’ of 
the Geological Society of Cornwall of 1819, 1820, and 1822 record 
some of the results, showing the gradual increase of temperature in 
depth. This was contested at home and abroad, or attributed to 
the presence of miners and their candles, which Humboldt at first 
did in the Mexican mines, while afterwards Humboldt had great 
difficulty in persuading Arago even to allude in the ‘‘ Annales De 
Chimie” to Mr. Fox’s researches. His conclusions as to the ratio 
of increase of heat in depth have been more or less confirmed, 
however, by subsequent observers in different parts of Europe, and 
at greater depths. 
‘‘The mean result from his table of observations, showing an 
increase of 5° Fahrenheit for a depth of 300 feet, or 1° Fahren- 
heit for 60 feet, is so near to what may be taken as the average 
given by many observers in different parts of the world, as to im- 
press one with the importance of such a contribution to science, at 
a time when not only had ‘public opinion’ a great objection to 
these views, but certain insufficiently practised experts joined in 
denying them.” Mr. Fox in his first essays on this important 
subject was singularly modest and tentative in its treatment. He 
suggested merely that the warmth of mines did not appear to have 
received the attention it deserved; and without entering into 
speculation on the exciting cause, or the extent of the internal 
heat, suggested the probability that “the ascent of warm vapour 
may produce the high temperature in mines; and that its effect is 
more or less considerable in proportion to the facility with which 
it finds a passage upwards.” Here then, in addition to the enuncia- 
tion of the general principle, the variations and anomalies which 
attend its manifestation were at once accounted for. By no one 
was Mr. Fox more ably supported in his argument than by our late 
distinguished member Mr. W. Jory Henwood, r.r.s., who brought 
an immense mass of exact observations to bear upon the point, 
which it was impossible to gainsay. And it is now beyond question 
‘that to Mr. Fox was thus due the first discovery and statement of 
