524 MR. 0. W. RICHARDSON ON THE ELECTRICAL CONDUCTIVITY 
These numbers when plotted against one another on squared paper yield curves 
very like the current temperature curves for platinum (fig. 4). They have not, 
however, been inserted, since they are much the same as the current-temperature 
curves for carljon (fig. 13, p. 52G), which have been plotted from the same observations. 
Just as in the former experiments, the current was never found to be a function of 
the electromotive force alone, so also here the cooling curves never exactly coincided 
with those obtained as tlie temperature of the filament was raised. This was partly 
due to the permanent change in the resistance of carbon produced by heating.^ It 
was attempted to correct for this by taking, instead of the ratio of the resistance at 
moment to the original resistance at 11° C. l)efore commencing the experiment, the 
ratio to the resistance which the filament would possess if at a tenqDerature of 11° C. 
at that moment. The permanent change in the resistance was assumed to be 
proportional to the rate at which the resistance changed during an exj^eriment, the 
conditions being kept, as far as possible, constant. In this way it was possible to 
obtain by extrapolation the resistance which the filament would j)ossess if allowed to 
cool down to 11° C. at any stage during the experiments. That this process brings 
the two curves more nearly into coincidence will Ije seen at once on comparing the 
numljers in columns I., VI., and VII. of the following table. In this case the 
potential on the filament was — 204 volts, and the heating current was run at 
constant voltage. The results of these corrections are shown in the accompanying 
taifie :— 
1. 
11. 
HI. 
IV. 
V. 
VI. 
VII. 
VIII. 
Saturation 
current, 
1 = 10-7 
ampere. 
Heating 
current, 
amperes. 
Initial 
resistance 
proportional 
to 
Amount 
resistance 
decreased 
during 
experiment. 
Corrected 
zero 
resistance 
ir C., 
proportional 
to 
Ratio of 
resistance to 
corrected 
zero 
resistance. 
Ratio of 
resistance to 
original 
zero 
resistance. 
Pressure, 
millim. 
1-7 
•59 
1755 
0 
2910 
•604 
•604 
5-2 
•64 
1726 
0 
2910 
•594 
•594 
•003 
20-7 
•69 
1698 
0 
2907 
•584 
•584 
_ 
46-5 
•735- 
1682 
1 
2901 
•580 
•578 
•008 
118 
•78 
1664 
2 
2889 
•576 
•572 
_ 
294 
•83 
1645 
2 
2877 
•573 
•566 
•02 
735 
•89 
1624 
2 
2865 
•567 
•559 
__ 
310 
•87 
16.37 
2 
2853 
•574 
•563 
•035 
145 
•84 
1646 
3 
2835 
•581 
•566 
_ 
72 
•81 
1654 
2 
2823 
•586 
•568 
•04 
34-6 
•79 
1665 
1 
2817 
•592 
•572 
_ 
17-3 
•76 
1675 
1 
2811 
•596 
•576 
•035 
8-3 
•72 
1687 
1 
2805 
•602 
•580 
•03 
* Le Chatelier, ‘ Journal de Phys 
ser. 3, vol. 1, p. 185. 
