THE ROYAL SOCIETY. 
1841. No. 49. 
June 17, 1841. 
The MARQUIS OF NORTHAMPTON, President, in the Chair. 
The Right Honourable Lord Crewe, James Alderson, M.D., and 
Edward James Seymour, M.D., were balloted for, and duly elected 
into the Society. 
The following papers were read, viz. — 
1. “Experiments on the electric conditions of the Rocks and 
Metalliferous Veins (Lodes) of Longclose and Rosewall Hill Mines 
in Cornwall.” By William Jory Henwood, Esq., F.R.S., &c., Se- 
cretary of the Royal Geological Society of Cornwall. 
The experiments, of which the results are given in this paper, were 
undertaken with the view of determining whether it was in conse- 
quence of the imperfections of the galvanometers, or other apparatus, 
employed, that Mr. R. W. Fox, and other experimenters, had been 
unable to detect the presence of electricity in the tin veins of Corn- 
wall. The mode of experimenting was in principle the same as that 
pursued by Mr. Fox, namely, that of placing plates of metal in con- 
tact with the points to be examined, carrying wires from the one tc 
the other, and interposing a galvanometer in the circuit. The plates 
employed were of sheet-copper and sheet-zinc, and they were about 
six inches long, and three inches and a half wide. The wires were 
of copper, one twentieth of an inch in diameter, and the same that 
had been used by Mr. Fox. 
The tabular results of these experiments show that both the gra- 
nite and the tin vein at Rosewall Hill mine, and also the greenstone 
and the copper vein in that of Longclose, present unequivocal traces 
of electric currents, whether different parts of the same veins or va- 
rious portions of the same rocks were examined. 
It also appears, from these experiments, that the nature and posi- 
tions of the small metallic plates employed materially affect, not only 
the intensity, but in some cases also the directions of the currents ; 
and also that there is a considerable difference in the results when the 
same plates of metal are placed on different ingredients in the veins, 
even though these may be in immediate contact with each other. 
