208 
Proceedings of the Royal Society 
(2.) Mr A. Brebner made during last winter a number of careful 
determinations of the polarisation of electrodes of various materials 
in commercial sulphuric acid of various strengths and at various 
temperatures. The process employed was essentially the same as 
that described by me in the Proceedings B.S.E. for May 31, 1869. 
The following are means of many experiments : — 
The results of such experiments cannot be expected to be very 
accordant, but, if the means above given may be trusted, the 
polarisation is less for 1 acid to 20 water than for either stronger 
or weaker acids ; and it also falls off more slowly with increase of 
temperature. 
(3.) Messrs P. W. Meik and J. Murray made many observations 
with an electric balance, and resistance coils, to test the change of 
electric resistance produced in a wire by extension. The wires 
tested were of two specimens of copper — one of high, the other of 
very low, conducting power. They were taken of equal gauge and 
of such lengths as to have almost equal resistance ; one was associ- 
ated with a 10 B.A. Unit coil as one side of the balance, the other 
had associated with it a box of resistance coils initially set at 10 
B.A.U. The value of the galvanometric scale was determined in 
each experiment by increasing by a small known amount the 
resistance of the coils in circuit. The results are not yet quite 
reduced ; as we require to know the linear extension, and (if possible), 
the cubical contraction, of each wire produced by the appended 
weights. But, even in their present state, they appear to be of 
some consequence, as they show changes of conducting power almost 
exactly proportional to the weights appended, but singularly differ- 
ing in absolute amount for these dissimilar specimens of copper. 
Acid to 
Water. 
Tempera- Polarisa- 
tnre C. tion. 
Platinum Electrodes. 
Polarisa- Acid to 
tion. Water. 
Tempera- Polarisa- 
tnre C. tion. 
