TEMPEEATUEE ON THE ELECTEIC CONDUCTING POWEE OE METALS. 
millims. long. With very little practice the temperature could be read off to 0°'l C. 
with accuracy. This thermometer was calibrated by ourselves, and afterwards com- 
pared with a normal thermometer from Kew Observatory, for which we were indebted 
to the kindness of Mr. Balfour Stewart. The corrected readings of our thermometer 
agreed perfectly with those of the Kew thermometer. 2. A normal thermometer from 
Messrs. Negretti and Zambra, divided into 0°'2 C. This was compared with the Kew 
thermometer and found to be correct. The boiling- and freezing-points of the thermo- 
meters were taken at intervals, and the necessary corrections made. 
As the hght in the room where the experiments were made came from above, and as 
the thermometers lay horizontally in the trough, by placing the eye in a position so that 
the division on the thermometer covered its reflexion on the column of mercury, all 
error of parallax was avoided. The thermometers were always read off with the help 
of the magnifying glass A through the oil in the glass tube d, so that the whole of the 
column of mercury had very nearly the temperature of the bath. 
The normal wires were made of annealed german silver, and their resistances deter- 
mined by comparing them with a hard-drawn wire of the gold-silver alloy They were 
soldered to two thick copper wires, varnished, and when used placed in the cylinder G, 
filled with oil, in which a thermometer hung. The temperature of the oil was taken 
immediately after each obseiwation, and the conducting power of the normal wire cor- 
rected by the use of the formula 
A=7•803-0•0034619^-f0•0000003951^^ 
which was found by the determination of the conducting powers, at different tempera- 
tures, of a piece of wire from the same coil as that from which the normal wires were 
cut. In this paper we have taken as unit the conducting power of a hard-drawn silver 
wire at 0° C. = 100 (that of the hard-drawn gold-silver alloy at 0° being =15'03), in 
order to be able to compare at sight the present determinations with those made by one 
of us a short time agof. 
Before beginning a series, as already stated, all the ends of the wires dipping in the 
mercuiy-cups were re-amalgamated, and the zero-point of the scale redetermined. The 
current from the cell D was only allowed to pass through the apparatus for a second or 
two at a time, for fear of heating the wires, &c. 
From 0° to 100° seven intervals were chosen at which observations were made, viz. 
12°, 25°, 40°, 55°, 70°, 85°, 100°. With a little practice the flames of the 6-Bunsen 
burner could be regulated so as to come within a degree or two of the above tempera- 
tures. For about five minutes before, and whilst making the observations, the oil in 
the trough was stirred, one observer being at the trough whilst the other determined 
the resistances. Four observations at each interval were generally made on heating the 
wire to 100°, and again four at each interval on cooling (where this was not the case it 
will be mentioned with the series). 
* Philosophical Magazine, February 1861. 
t Philosophical Transactions, 1858 and 1860. 
