[August, 
584 Proceedings of Societies. 
therefore considered terrestrial magnetism to be still a mystery. 
He had also thought that the aurora borealis might be explained 
by supposing the upper regions of the earth’s atmosphere eleClri- 
fied. The winds carrying the upper strata towards the poles, 
electricity would condense there. This hypothesis is tenable still. 
Prof. Ayrton said that whether or not the new theory of mag- 
netism should be so rejected depended on whether or not Prof. 
Rowland’s calculations, or those of himself and Prof. Perry, 
were wrong. It had been found by Sir William Thomson, from 
experiments at Arran, that the earth was electrified with respeCt 
to the air, and that there is a difference of potential of 30 volts 
between earth and air for each foot of ascent. This gave 
1360 Xio 12 centimetre-gramme second electrostatic units as the 
potential of the earth. The new theory required the potential 
to be 101 1 X io 11 , or supposing the earth to be solid iron, or about 
14 times more, a wide margin. 
Prof. Rowland said he had not seen the calculations of Profs. 
Ayrton and Perry yet; but he believed his results to be correCl, 
as he had checked them in various ways. 
Mr. Bailley exhibited a modification of Arago’s experiment, in 
which a copper disc is caused to rotate continuously by changing 
the polarity of four eleCIro-magnets underneath by a revolving 
commutator. 
Mr. Conrad Cooke exhibited a single voltaic element showing 
the internal current. This is done by forming the glass vessel 
containing the element into a helical tube between the poles, and 
hanginga galvanometer needle in the interior of the helix: the 
internal current deflects the needle. 
