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of Edinburgh , Session 1875 76 . 
by the ordinary balance method. That no errors were caused by 
thermo-electric effects was proved repeatedly during the experi- 
ments by completing the circuit without the galvanic cell, when no 
current was shown on the galvanometer. The results obtained for 
the nickel entirely agreed with what had been anticipated from the 
thermo-electric properties. For, when the conductivity is plotted 
in terms of the temperature, the curve shows a sudden change in 
direction at a temperature of about 149° C. (300° F.), indicating 
that there is at that point a sudden change in the rate of alteration 
of the conductivity with change of temperature. The curve ob- 
tained for nickel can be very well represented by two straight lines 
inclined to each other at an angle of about 9°, while the curve got 
for the platinum wire is strictly a straight line. 
That no part of the effect was due to the conductivity of the 
oil was amply proved by the following experiment : — 
Two pieces of platinum foil, each having a surface of 2*5 square 
inches, fastened to the ends of copper wires, were plunged in 
the oil when it was at a temperature of 550° F., and were kept 
a quarter of an inch apart; the resistance of the oil between them 
was then measured, and was found to exceed 9 megohms, while 
the resistance on causing them to touch fell to a small fraction of 
an ohm. 
After a series of experiments had been made with the nickel, 
the whole spiral was heated to a white heat in the flame of a Bun- 
sen burner, and allowed to cool in the air ; another series of ex- 
periments was then made on the conductivity, but no change was 
observed. 
The following tables contain the observations for two of the 
experiments, side by side with the values of the conductivity, calcu- 
lated on the supposition that the curves are best represented 
by straight lines — the platinum being represented by a single 
straight line, while the nickel is represented by a broken line. 
The calculated and observed values, it will be seen, agree very 
closely with each other, except where a divergence is to be ex- 
pected, namely, at the intersection of the two lines (nickel). The 
equations were taken from the lines obtained by plotting the con- 
ductivity in terms of the temperature. R is the resistance in 
thousandths of an ohm, t the temperature in degrees F. : — 
VOL. IX. 
R 
