59 
1908-9.] On the Kecalescence Temperatures of Nickel. 
galvanometers, these copper junctions being kept in test-tubes of alcohol 
surrounded by melting ice. 
The galvanometers were both of the D’Arsonval type. The one used 
in the differential circuit was of 1098 ohms resistance, and of such sensitive- 
ness that it gave a deflection of inch with 1 volt on 3950 megohms 
at 40 inches distance from the scale, and although not aperiodic it was not 
far from being so. The galvanometer of the temperature circuit was more 
sensitive than I required, and was therefore used with an external resistance, 
as its scale had to register from 100° to 1000°. 
Preliminary experiments showed that the nickel did not oxidise in the 
furnace to an extent likely to affect any exhibition of recalescence, so 
I did not think it necessary to keep the metal in a non-oxidising gas. 
The scale of the temperature galvanometer was calibrated by making 
use of the known boiling-points of water, naphthaline, and sulphur, and 
determining the position of these known temperatures on the scale, the 
error limit amounting to ±T nun., or less than * 5 °. The boiling-point of 
naphthaline was taken as 218°, and that of sulphur as 444‘5°. An open V. 
Meyer tube 48 cm. long, with a bulb 8 cm. in diameter, and jacketed outside 
with asbestos, was used to boil the naphthaline and sulphur in, and the 
thermo-junction, protected by a thin- walled Bohemian glass tube, was lowered 
to within 4 cm. of the boiling liquid. The vessel used for the water was a 
wide-necked flask 17 cm. in diameter, fitted with an escape tube and lined 
outside with asbestos ; precautions to prevent bumping were observed, and 
the thermo-junction inserted as before. A curve drawn through these three 
determinations, as plotted on a temperature deflection diagram, then furnished 
the means of getting the temperature corresponding to any deflection on the 
galvanometer scale. 
The general procedure was to heat up the furnace and contents slowly 
in about If hours to about 1000°, then shut off heating current and connect 
up galvanometers. During the cooling, readings of the two galvanometers 
were taken simultaneously at equal falls of temperature — about 4J° — as 
registered by the temperature galvanometer, photographic or other self- 
recording appliances not being available. 
In the cooling curves drawn to detect recalescences, the deflections of 
the differential-circuit galvanometer were plotted as abscissae, and as 
ordinates the actual temperatures of the nickel determined by the deflec- 
tions of the temperature galvanometer. These curves are rather complex 
in form, and as they might be expected to be simpler the more uniform the 
temperature of the furnace at the beginning of the cooling, I at first kept 
the furnace at its maximum temperature for about half an hour, in order to 
