OBITUARY NOTICES. 435 
the great law of the progressive increase of the temperature of the 
earth in depth. 
These enquiries led Mr. Fox to take up further investigations 
into the then utterly unexplored region of terrestrial electricity and 
magnetism. He had speculated that in the earth there are the 
conditions of a voltaic pile, giving rise to electric currents ; and he 
proved this by descending into some of the deepest mines, where 
he had the pleasure of seeing the needle of the galvanometer de- 
flected when wires connected it with different parts of a vein. In 
June, 1830, Mr. Fox’s paper on the electro-magnetic currents in 
metalliferous veins was read before the Cornwall Geological Society. 
He stated that the temperature of the earth must at considerable 
depths produce greatly superheated steam, and sometimes occasion 
earthquakes. It might also convey minerals in solution to be 
deposited by electric currents in fissures (whether enlarged from 
time to time, as many have been, or not), but mainly in those 
which ran more or less at a right angle to the magnetic meridian 
of the period. His formation by electrical action of mineral veins 
in clay illustrated and confirmed his views. 
When M. Ampére inferred that the direction of the terrestrial 
magnetic meridian is due to electrical currents circulating from east 
to west, Mr. Fox argued that such currents would tend to course 
through east and west fissures, in which saline solutions were 
present, and that in the decomposition which would thence result 
the metals or bases would be determined towards the electro- 
negative contiguous rocks, and the acids to the electro-positive. 
He was not only in this way the discoverer of the electricity of 
mineral veins, but the inventor of the deflector dipping needle, by 
which he determined the magnetic dip and intensity in various 
places in England and on the Continent ; and his last public work 
was the final adjustment by his own hands of the dipping needles 
for the Arctic expedition under Sir George Nares. 
Steinheil, in 1838, observed that, with one wire only, the electric 
circuit was completed through the earth. About the same time 
Mr. Fox independently discovered this fact, of the greatest im- 
portance in telegraphy, whilst experimenting with the electric wire 
of his young friend, the late Mr. R. Barclay, jun., at Leystonstone, 
and communicated the fact to Professor Wheatstone. Space does 
not admit of further reference to his various papers in the 
“ Transactions” of the Royal, Polytechnic, London, and Cornwall 
