22 MEASUREMENT OF HIGH TEMPERATURES. 
SUPPLEMENTAL. 
Let me here add, before passing cm, that since this manuscript left 
my bands some additional work has been done in high-temperature 
thermometry. A form of standard air thermometer has been devised 
and is being made. A torsion galvanometer suitable for the measure- 
ment of thermo-electric powers, such as are here encountered, has also 
been constructed. To test the efficiency of this instrument I made a 
series of measurements on the variation of boiling points with pressure, 
using the re-entrant porcelain crucible and the closed boiling tube 
figured below (Chap. II, Figs. 14a and 11a). The results for mercury, 
sulphur, cadmium, zinc, and bismuth, covering an interval of some 
1,500° C, are important, inasmuch as they indicate the probable truth 
of the principle of Groshans. (Pogg. Ann., vol. 78, 1849, p. 112.) 
I will advert to the independent method of standardizing a non-in- 
glazed re-entrant porcelain air thermometer bulb, by thermal com- 
parison with a re-entrant glass thermometer bulb of known constants. 
Such comparison is to be made above 300° to obviate all moisture and 
condensation errors, and either directly in the elliptic revolving muffle, 
or indirectly through the intervention of the same thermo-couple. The 
difficult* estimation of the volume of the non-in-glazed bulb is thus 
superfluous. 
Again, to insure union, the gradual sagging of a weighted porcelain 
stem, the lower end of which has been heated to the viscous condition 
before the oxyhydrogen blow-pipe, into the heated neck of a re-entrant 
in-glazed bulb on the revolving table, has suggested itself. Similarly, 
atmospheric pressure may be brought to bear externally on viscous 
parts of bulb or stem. (Of., p. 175.) 
Regarding literature, I may briefly refer to a recent critical work by 
G. H. Bolz (Die Pyrometer, etc., 70 pp., Berlin, J. Springer, 1888), and 
M. H. Le Ghatelier has recently extended his valuable pyrometric re- 
searches in various directions. 
C. B. 
Boston, /Sept. 1, 1889. 
Note.— The thermo-dynamic i masons referred to on page 18 are briefly these : In the notation of 
Clausius (Warnie-theone, "Jd ed., I, Braunschweig, 1876, p. 172), the first and second laws together 
Kail to the equivalent of James Thomson's equation: dT/dp=T(<r— t)/Et' ; and the second law gives 
the equation dr'fdT=c'—L'-\-r'/T. Starting with these equations of fusion, I purposed to formulate 
the relation between melting poiDt and pressure, /(p, T) — 0, from direct experimental measurements, 
using the relation only within the pressure limits of the experiment. From this point it is difficult to 
proceed, for it is next necessary either to measure <r — t as a function of pressure and temperature, or 
to measure the corresponding relation of r> . In addition to the above equations the more general re 
lations 
T d p v dp T (d p v\*/d T V 
C ~ C p~ E dT dT and c v= c p+E Xdf> I ~dp 
are available. 
(G70) 
