Measure of Resistance to Galvanie Currents. 35 
removed when the mercury had slowly passed entirely through 
the windings of the tube. | 
As mercury is not to be found in the list of metals the altera- 
tion of whose specific resistance by heat has been determined by 
Arndtsen*, this deficiency had first to be remedied. This was 
effected by Dr. Esselbach, by means of the apparatus already 
described. The resistance of one of the spiral tubes was com- 
pared with that of the straight tube 2, first at the temperature 
of ice-water, and then when the temperature of the spiral was 
raised. If w represent the resistance of tube 2 (which according 
to Table III. is 498-7), and w, the resistance of the spiral tube, 
then, since the resistance of the conducting wires was rendered 
equal for both tubes, and was equivalent to that of 11 cubes of 
mercury 1 millim. each way, we had 
wt+ll oa 
w+ll 8 
where a and & represent the pieces of platinum wire of the bridge 
when no current passed through the galvanometer. This was 
the case when 
a_ 8113 
b- 688°7’ 
whence w = 219°4, 
The temperature of the straight tube was now maintained at 0° 
by means of melting ice, while the temperature of the water sur- 
rounding the spiral was raised. In the following Table, ¢ indi- 
cates the temperature of the straight, and ¢, of the spiral tube, 
a and b the lengths of wire read off when the currents were equal, 
y the required coefficient calculated according to Arndtsen’s 
formula, 
w(l+yt)+ll_a@ 
w(l+y)+ll 68 
Table V. 
te ae a. b. UP 
0 47-0 C. | 8204 679:5 | 0-000964 
0 34:5 318-0 682-0 | 0-000960 
0 165 3146 685-4 | 0:000981 
From this it appears that, of all simple metals, mercury is 
that whose resistance is least increased by an increase of tempe- 
rature. 
By means of the coefficient y, the resistances of the two other 
spirals A and B were determined, which were afterwards used 
* Poggendorff’s Annalen, vol. ci. p. 1. 
D2 
