32 
Proceedings of the Royal Society 
2. Laboratory Notes. By Professor Tait. Communicatee!, 
in his absence, by Professor G. Forbes. 
1. On the Eelation between Thermal, and Electric, Conductivity. 
Reference was made to a previous paper by the author (Proceed- 
ings, 1867-8, p. 309), in which an attempt was made to apply to 
this subject the Theory of Dissipation of Energy. 
Some years ago, a bar of German silver was procured, at the 
expense of the British Association, for the purpose of ascertaining 
whether its thermal, like its electric, conductivity is little altered by 
change of temperature. With this, Forbes’ experiments have been 
carried out carefully through very great ranges of temperatures. 
The exceedingly laborious calculations necessary to a complete 
determination are not yet carried out; hut, by a rough graphic 
method, it lias been ascertained that the alteration of conductivity, 
by rise of temperature, is at least very small compared with that 
observed in iron under the same circumstances. 
2. On Electric Conductivity at a Red Heat. 
This was a mere preliminary notice of what promises to be at 
once an interesting and an extended inquiry, to which I have been 
led by some recent results in thermo-electricity. At present, it may 
be stated that at, and above, a red heat the electric conductivity of 
iron seems to fall off much faster with increasing temperature than 
that of platinum. To such an extent does this take place, that I 
have endeavoured (as yet, however, unsuccessfully) to form a cir- 
cuit in which the main resistance is an iron wire, and to obtain a 
maximum current by gradually shortening the wire. The fall in 
conducting power seems so very marked that some of it will re- 
main, even I believe when allowance is made for the oxidation of 
the iron. I have ordered a special apparatus for the purpose of 
avoiding this source of uncertainty. 
3. On the Thermo-Electric Relations of Pure Iron. 
By the kindness of Dr Russell, of Bartholomew’s Hospital, I have 
been enabled to experiment upon a ribbon of pure iron prepared by 
