SIS Proceedings of the Cambridge Philosophical Society. 
which it appeared that the effect was considerably less than what 
would be produced in atmospheric air of the same density. The 
cause appears to depend partly on the tenuity of hydrogen gas, 
and partly on the rapidity with which the pulsations are conveyed 
through this very elastic medium. 
On the Connection between Galvanism and Magnetism. By 
the Rev. J. Cumming, M. A. F. R. S., Professor of Chemistry. 
— Before reading his paper, the Professor repeated the electro- 
magnetic experiments of Professor Oersted, in presence of the 
Society. The first part of the paper contained an account of 
the effects of a wire connecting a large Zinc and Copper plate, 
on two magnetic needles, one moving horizontally, the other 
vertically ; the connecting wire being bent into the form of a 
circle, and the needles applied to it at different azimuths. The 
direction of the galvanic current was shewn to be such, that a 
wire connecting the zinc and copper -plates tended to place itself 
at right angles to the magnetic meridian, which appeared ex- 
perimentally, by suspending a pair of very small plates. An 
instrument was then described for detecting weak galvanic 
action, by its effects on the magnetic needle. It was found that 
the magnetic influence could not be transmitted between a pair 
of plates through any non-metallic medium ; but, on making 
the circuit through a tube filled with acetate of lead, the needle 
began to be affected, when the arborescence of the revived lead 
had formed the metallic connection. On using connecting-wires 
of different lengths and diameters, it appeared that the magne- 
tic influence was transmitted through large wires, though of 
considerable length, provided they were solid, more readily 
than through small ones, however short. An analogous effect 
was found to be exhibited on connecting the poles of a magnet 
by pieces of iron, of different lengths and thickness. The pa- 
per was concluded by contrasting this analogy with the opposite 
effects observed in the transmission of common electricity. 
May 7. — On the Geology of the Lizard. By the Rev. A. 
Sedgwick, M. A. F. R. S. F. C. P. S., Wood wardian Professor. 
— In the early part of this paper, the Professor gave a short 
description of the external appearance of the country, as far as 
it appeared to be connected with its mineral structure. He 
then entered into details respecting the phenomena presented by 
