198 
MEASUREMENT OF HfGH TEMPERATURES. 
| BULL. 54, 
favorable cases be known within 4 per cent. These results are also; 
in keeping with Table 45, above. Fortunately it is feasible to measure 
v" 
- with the accuracy here required, as well as to sufficiently exclude 
the effect of temperature. 
A careful survey of the sources of error just discussed shows how ex< 
ceedingly difficult the measurement of high temperatures, with an accuj 
racy of 1 : 1000, really is. Quite aside from these discrepancies and the 
arbitrariness of a and /?, the lag error, the environment error, the moistj 
ure error, the error due to the permeability of porcelain and to diffusion 
of some gases through it, and the error of unknown flaws, have yet to bd 
discussed. In the face of these serious difficulties I was therefore pleased 
to find that greater harmony prevails in the established data for higa 
temperatures than there was reason to anticipate at the outset. I maj 
state here that a more rigorous discussion of errors is to be made iiij 
treating the constant-pressure method, since this method is very muca 
better adapted for high- temperature measurement than the presenl 
one. I will (p. 228) give the methods of allowing for all arbitrary errori 
and such as are not considered here. 
CONSTANT-VOLUME THERMOMETER — EXPERIMENTAL RESULTS. 
Earlier results. — The measurements were commenced with the forms 
of bulb shown above in Fig. 32. These bulbs are not glazed internally} 
but consisting Of but a single piece they can be manipulated witJ 
greater facility than the others, in which soldering must precede tn 
temperature measurement. To obtain some idea of the availability m 
the unglazed bulbs, I made a number of measurements of the boiling 
point of water. Examples of the results obtained are given in Table 
48, in which H and h are the tension of the air at 100° and at 0°« 
centimeters of mercury. It is to be remarked that h is here directl$ 
obtained by surrounding the bulbs with melting snow for many hours. 
By way of comparison, the same temperature T is also measured by» 
glass air thermometer. 
Table 48. — Moisture error of unglazed bulbs. 
Xo. 
ho 
M 
T 
Remarks. 
Glass : 
cm. 
cm. 
cc. 
Xo. 1 .... 
76.70 
104. 47 
100 
Porcelain : 
Xo. 1 .... 
73.50 
141.90 
256 
Bulb not specially dried. 
Xo. 2 . . . . 
Xo. 3 .... 
72. 40 
7G. 46 
115. 00 
119. 58 
162 
155 
f Both bulbs dried by repeated exhaus- 
-[ tion after calibration with water. 
( Bulb at 100° during drying. 
Xo. 4 . . . . 
72.62 
102.98 
115 
Bulb carefully dried X>y repeated ex- 
haustion with mercury air-pump. 
Bulb and stem at 100°. 
(852) 
