110 
MEASUREMENT OF HIGH TEMPERATURES. 
PRACTICAL CALIBRATION. 
[bull. 
Investigation of data. — Instead of extending these experiments im 
higher temperatures and determining further data for the fire-clay a j 
paratus, it will be expedient to actually calibrate a series of element 
Such experiments will show both the constancy of the divers boiliE 
points as regards time, as well as their absolute correctness as cor 
pared with the data of Chapter I. Indeed, the degree of identity e: 
hibited by distinct series of data obtained almost a year apart, I 
thoroughly different methods and under different circumstances in a 
other respects, will be the best available criterion of the validity of tt 
said series of results. Hence the following table is given with conside 
able fullness. The boiling points taken are zinc (930°), sulphur (448 c 
mercury (357°), aniline (measured 187°), and water. All observatioi 
are made in time series ; and for the temperatures t and T of the cold an 
hot junctions, the electromotive force e microvolts was observed at tt 
time specified on the same horizontal row. The mean of these isolate 
observations being taken, the results are used for the calculation of tt 
constants a and b in equation (1) above, by the method of least squares 
a and b are inserted in the ninth column. The fifth contains the ca 
culated value of e, and its difference from observed e is given in tfcli 
sixth column. Finally, in the seventh and eighth columns are inserte 
the correction e 2 o— e and the value e 20 of electro-motive force whic 
hold for t=2i). In addition to these data the table contains value 
parenthetically inserted. These are derived from the constants for th 
calibration if carried only as far as the boiling point of sulphur, to th 
exclusion of zinc. Hence these constants, being derived similarly t 
the extrapolation constants of Chapter I, are at once comparable wit 
them. 
Table IS.— Calibration of thermo-couples Nos. 17, 18, 22, 35, 36. 
No. 
Mean. 
t. 
, 
° 0. 
° O. 
20. 4 
930 
20.4 
930 
20.7 
930 
20.8 
930 
21.4 
930 
21.4 
930 
21.8 
930 
22.0 
930 
22.5 
930 
22.7 
9.;o 
22.8 
930 
22.8 
930 
22.8 
930 
21.7 
930 
e ob- 
served. 
Micro- 
volts. 
9101 
9185 
9169 
9173 
9169 
9152 
9173 
9169 
9211 
9211 
9211 
9211 
9211 
9180 
<i calcu- 
lated. 
Micro- 
volts. 
Be. 
Micro- 
volts. 
Micro- 
volts. 
(764) 
Micro- 
volts. 
9101 
9185 
9170 
9175 
9176 
9159 
9183 
9182 
9227 
9228 
9229 
9229 
9229 
9190 
a and b. 
Microvolts. 
8. 049 
0. 002357 
Time 
h. n 
2 2' 
