58 Proceedings of the Royal Society of Edinburgh. [Sess. 
galvanometer and thus determines the temperature of this metal. 
Carpenter and Keeling used platinum as the “ blank ” metal or metal 
without recalescence ; but as platinum was not available, and I did not 
wish to work above 1000°, I used pure copper as being suitable for this 
purpose. 
A diagram of my arrangement is shown in tig. 1. FF represents the 
lagging of the furnace, and AB its porcelain tube ; C is a copper block, 
drilled with a hole for the insertion of a thermo-couple, and N the nickel 
block with two holes for thermo-couples ; D is the galvanometer for the 
double thermo-couple or “ differential ” circuit ; and T the galvanometer 
indicating temperature of N. 
An electrical resistance furnace made by the Cambridge Scientific 
Company was used ; it consists of a tube of English porcelain 62 cm. long, 
of diameter 4 cm., and lagged with asbestos to a diameter of 19 cm., this 
tube being heated electrically by a coil of platinum foil. 
The metal blocks were 2 cm. long and 3J cm. in diameter, drilled with 
holes 1‘3 cm. deep and *6 cm. in diameter; these were placed about 
•6 cm. apart in the centre of the furnace tube, the rest of the tube being 
loosely packed with asbestos, and under these conditions a cooling from 
900° to 180° occupies about 3J hours, the heating current being completely 
shut off. 
The thermo-junctions were of platinum and platinum-iridium wires 
welded together in the blowpipe; the wires of the “ differential ” circuit 
were ‘005 cm. in diameter, and those of the “ temperature ” circuit ‘02 cm. 
in diameter ; in each case the wires were insulated by means of thin 
porcelain tubes, and were soldered to copper leads to their respective 
