69 
electric) to overcome external resistance, is directly propor- 
tionate to the length of wire which it will melt. 
From a consideration of these results it will be seen that 
one of the fundamental elements which enters into the 
theory of Ohm is found wanting when that theory is applied 
to the estimation of the magnitude of currents generated in 
circuits entirely metallic. 
MM. Jamin and Roger, in a recent number of the Gomptes 
Rendus of the Academy of Sciences, have also pointed out 
the discrepancy here referred to in the application of Ohm’s 
theory to magneto-electric circuits. The author is, however, 
by no means prepared to admit the correctness of the views 
advanced by these physicists in their endeavours to recon- 
cile the facts observed, with established theory; besides 
which, other anomalies present themselves when the cus- 
tomary formulae are applied to magneto-electric circuits, a 
consideration of which must, as the author affirms, lead 
ultimately to the enunciation of laws much more general in 
their application than those with which we are at present 
familiar. 
MICROSCOPICAL AND NATURAL HISTORY SECTION. 
October 12 th, 1868. 
Joseph Baxendell, F.R.A.S., Vice-President of the 
Section, in the Chair. 
Mr. Henry Brogden forwarded three deposits of Diatom- 
acese for distribution amongst the members, viz., from the 
Galtee Mountains, Ireland, collected in 1868; from Levers 
Water, Coniston Old Man, collected in 1856 ; and from a 
stream near Half-Moon Bay, near Carrick-a-Rede, Antrim, 
July, 1861. 
