204 
MEASUREMENT OF HIGH TEMPERATURES. 
[bull. 54 
instances nearly 100° wide and the boiling points of zinc fluctuate be 
tween 925° and 995°. 
Later results. — Following the suggestion of the results contained or 
pages 199 to 204, 1 made the following series of additional comparisons 
The bulb used is still the non-re-entrant form, not glazed internally 
Great care was taken to dry it thoroughly by heating the bulb to 100°,, 
and then exhausting the air to a few tenths millimeter. After being: 
treated in this way the bulb was filled with air, dried over anhydrous 
phosphoric acid. In the last two series 7/ is calculated from the tension 
observed at 100°. Special care was taken with the cathetometric meas-l 
urements. Tbe series of temperatures is ascending. The influx of gas; 
is gradually increased by means of a graduated stopcock, and the cali- 
bration measurements are made after each increment as soon as the 
temperature has again become stationary. In this way not only mayv 
any number of degrees of constant temperature be obtained, but the 
mean rate at which temperature increases may be reduced as near 
zero as is desirable. If therefore one observer 1 notes the instant of 
contact between the upper meniscus of the manometer and the fiducial 
mark, the other observer may note the corresponding cathetometer 
reading of the lower meniscus for the same instant. From a comparison 
of the following results as a whole I infer that in proportion as the tem- 
perature of the muffle increases, equality of temperature for all points 
of its inner surface more nearly obtains. This is due to the fact that at 
high temperatures its heat conduction is better. For low temperature 
calibrations it is therefore advisable to use a muffle cooling from red heat 
in a closed furnace. In the tables e 20 has been calculated for £=20°. 
The actual temperature (t) of the lower junction is given in Table 52 
for each case. 
Table 52. — Comparison of air thermometer and thermo-couple. 
ho = U.6fr m . Bulb No. 4. 
Thermo-couplo No. 37. 
* 
T 
Time. 
* 
^20 
Time. 
cm. 
o(7. 
hours. 
°a 
microvolts. 
hours. 
27.35 
241 
2.78 
28.0 
2545 
2.78 
30.25 
297 
2.88 
28.0 
2941 
2.84 
31. 68 
324 
2.99 
28.0 
3060 
2.90 
33.25 
354 
3.14 
28.0 
3283 
2.97 
34.32 
375 
3.35 
27.8 
3792 
3.40 
34.32 
375 
3.42 
27.8 
3780 
3.43 
41.47 
512 
3.73 
27.8 
3780 
3.45 
42.33 
529 
3.78 
28.3 
5475 
3.68 
48.49 
648 
4.00 
28.3 
5820 
3.75 
49.99 
678 
4.07 
28.3 
7132 
3.93 
50.86 
694 
4.11 
28.3 
7706 
4.02 
57.80 
831 
4.31 
28.3 
8015 
4.08 
1 Mrs. Anna H. Bams assisted me in this work. 
(858) 
