60 Proceedings of the Royal Society of Edinburgh. [Sess. 
get the thermal conditions as steady as possible ; but this was not found to 
simplify the form of the curves, and subsequently, and in the case of the 
curves illustrated, the cooling was started immediately after the maximum 
temperature was reached. 
The general form of the cooling curves may now be discussed. Under 
ideal conditions, with two similar pieces of the same metal, similarly 
situated in a furnace cooling uniformly, and initially at a uniform tempera- 
ture throughout, the metals will always be at the same temperature during 
cooling, and the galvanometer of the differential circuit will be continuously 
at zero, so that the curve will coincide with the temperature axis. If we 
consider, however, the actual conditions under which I worked, we see that 
with two pieces of different metals, though neither of them metals which 
exhibit recalescence, in general there will be a difference of temperature 
between them throughout the cooling, as the furnace is not initially uniform 
in temperature throughout. Also this difference will be of different magni- 
tude and sign according to the actual distribution of temperature in the 
furnace, while it will also be affected by the relative sizes and natures of 
the bodies, position in the furnace, and surroundings generally, so that the 
exact form of the curve cannot be foreseen. We can, however, say that (1) 
the initial abscissa will in general differ from zero, since there will in 
general be an initial difference of temperature between the metals ; (2) the 
curve must finally arrive at the temperature axis, since the two metals must 
finally both come to room temperature ; (3) if one of the metals cools more 
rapidly than the other, and is initially at the higher temperature, the curve 
may run down more or less steadily to the temperature axis, or it may cut 
the axis before the final temperature, and attain a maximum on the other 
side, before returning to the temperature axis again at the room tempera- 
ture ; (4) if the metal which cools more slowly is initially at the higher 
temperature, this difference of temperature may increase at first, though 
finally it must become zero at room temperature as before ; (5) the maximum 
points indicated above will not occur at any definite temperature, but may 
correspond to a high or low temperature ; in fact, the maximum difference 
of temperature between the metals will depend on their initial difference of 
temperature and on the conditions under which the cooling occurs, which 
will vary according to the distribution of temperature in the furnace. 
The result of the occurrence of recalesence in one of the metals may be a 
rise in temperature of that metal, or at least a slower rate of fall than there 
would otherwise have been, and the effect in the curve will be a more or 
less sudden change of slope. If the recalescence be of small range, the curve 
will immediately return to approximately its former slope, and the result 
