ON THE MEASUREMENT OF TEMPERATURE. 
151 
A^a])oni‘ Pressure of Liquid (5xygeu. 
Pressure on gas 
in thermometer. 
Temperature of 
dead-space. 
Temperature 
of stem. 
Vapour pressures 
of 
licpiid oxygen. 
Tempt 
Found. 
.rature 
Calculated. 
millims. 
“C. 
° lie. scale. 
inillims. 
° He. scale. 
° He. scale. 
*307-70 
16-0 
103 
750-5 
90-11 
90-08 
1307-94 
16-5 
105 
755 - 5 
90-18 
90-15 
305-00 
17-1 
98 
692-0 
89 - 32 
89 - 32 
300-45 
17-1 
98 
600-5 
87-99 
88 - 02 
291-95 
17-0 
89 
449-0 
85 - 47 
85-46 
301-05 
17-0 
97 
608-5 
88-17 
88-15 
292-30 
16-8 
78 
456-0 
85-58 
85 - 58 
in this experiineiit the vacuuni vessel surrounding tlie theruionieter bulb, &c., was 
first of all filled with nearly pure liquid oxygen. The ll(]uid was made to boil 
steadily by passing a current of gaseous oxygen into the liquid. Liquid air was 
added to the liquid oxygen to obtain the lower tein|)erature. Between tiie first and 
second observations the manometer and bidb containing the pure oxygen were 
exhausted and refilled. 
12. Treatment o f the Resnlte,. 
The figures given in the last column of the foregoing tables are the temperatures, 
corresponding to the observed ju-essures, taken from the smoothed vapour pressure 
curves shown in Plate 1. It will be observed that the points obtained l)y direct 
observation lie in every case very close to the curve, and that the difference between 
the observed and calculated temperatures rarely exceeds two or three hundredths of 
a degree. 
The results obtained by direct observation of tlie vapour pressures were smoothed 
by the method of Ramsay and Young {‘ Phil. Mag.,’ 188G, vol. 21, jj, 88 ; vol 22, p. 87), 
This method consists in calculating the ratios of the absolute temperatures 
T„, T/j, TV, T/, &c., for any pair of substances A aiid B corresponding to vapour 
pressures p, p', &c., and plotting the ratios T„/Tj, TV/T/, &c., against the temperature 
T,„ T/, as rectangular coordinates. The points so defined lie on a straight line, from 
which the temperatui-e corresponding to any pressure p for the substance B can be 
calculated, by first finding the temperature Tb coi'responding to that vapour pressure 
for the substance A, determining the value of the ratio Tb/Ti, and dividing the value 
of Ta by it. In smoothing our I'esults we took water as the second substance A. 
Two sets of ratios were obtained by this method, corresponding to the tempera- 
* The mean of two observations, 
t The mean of four observations. 
