104 MEASUREMENT OF HIGH TEMPERATURES, [bull. 5 
can be measured and with much less liability to error. If equation (1 
be solved with reference to T it follows that — 
4& 
where 
*-(J 
+f a 2-1 ; 
e=e+at+bt 2 . 
When many values of Tare thus to be found the computation is b: 
no means unlaborious. 
By keeping r constant, and varying B, a table can be calculated onct 
for all, for the function 
r 
in which a mean value is inserted for E. Such a table for frequently 
recurring values of the arbitrary constant r and for values of i£, increas 
ing in arithmetical progression with a difference of 1,000, is of greai 
service in facilitating the calculation of e. It insures greater exemp 
tion from error. A small correction for E is only necessary to correcl 
the interpolated results. 
Instead of applying a zero method like the present, it is of course 
permissible to use simplified processes in which currents only are meas- 
ured. A torsion galvanometer, such, for instance, as that actually used 
by Schiuz (1. c, p. 49), suggests itself. By the aid of my boiling tubes 
and crucibles the scale of such an instrument may be at once graduated 
in terms of the centigrade thermometer. Not only can this be done 
with a great degree of accuracy, but the thermal calibration of the 
galvanometer may be checked with ease as often as desired. There 
can be no doubt that for practical purposes this apparatus is exceed- 
ingly convenient. Nevertheless the measurement of electromotive 
forces by the zero methods here discussed retains an advantage over 
current measurement, because measurements of electromotive force 
made at one time may be at once compared with corresponding meas- 
urement made at any subsequent time. The data are easily expressed 
in terms of a fixed absolute standard, in other words. All this is much 
more difficult in the case of current measurement, even if it were as 
accurate, for current measurement brings in the arbitrary constants ot 
the galvanometer. 
EXPERIMENTAL RESULTS. 
Exploration for -constancy of temperature; water , aniline. — When the 
boiling tubes, Figs. 7 to 11, are to be used for temperature measure- 
ment, the chief point of interest is the degree of constancy attained 
throughout the length of the central tube into wftich the thermo-ele- 
tnent is to be inserted. To obtain the requisite data it is sufficient to in- 
sert a thermoelement, tbe constants of which are approximately known, 
into the tube mentioned, with the junction consecutively at different 
(758) 
