SEPTEMBER 3, 1897. ] 
nence of its constants in relation to Clark’s 
cell in the lapse of time, the instantaneity 
of its indications, the easy reproduction of 
destroyed couples, their relative insensitive- 
ness to furnace gases, the regular and sim- 
ple character of the temperature function, 
the sustained sensitiveness throughout all 
temperature ranges even quite into the fu- 
sion of platinum—all these facts are a suf- 
ficientif not overwhelming recommendation 
of the method. 
In speaking of long range temperature 
variables one is hardly permitted to over- 
look the remarkable work which has re- 
cently been done in the direction of low 
temperature, but with these subjects I am 
less familiar and can therefore only refer to 
in passing. The progress made in the 
subject is sufficiently evidenced by the 
growth of large low temperature laboratories 
throughout the world, laboratories which 
undertake ‘the cold storage’ of ‘cold storage,’ 
as it were, like those of Pictetin Berlin and 
Paris, of Dewar in London, of Kamerlingh 
Onnes in Leyden, of Olezewski in Krakau, 
and others. Dewar and Fleming have 
added to our knowledge of the probable 
constitution of bodies at the absolute tem- 
perature. Olezewski has found the critical 
temperature of hydrogen at —230° and its 
atmospheric boiling point at —243°. Dewar 
and Moissan have liquefied fluorine. There 
is much here which I must reluctantly 
forego. The hydrogen thermometer, the 
platinum balance (Callendar) and the 
thermo-couple are again doing excellent 
work in thermometry. 
APPLICATIONS OF PYROMETRY. 
Turning now to the applications of recent 
pyrometry, we meet first many series of val- 
uable data on melting points and similarly 
valuable data on the dissociation tempera- 
tures of chemical compounds. To these I 
merely refer, not being qualified to enter 
into chemical interpretations. High tem- 
SCIENCE. 
345 
perature boiling points have also been 
treated, and I will especially consider the 
case of the variation of metallic ebullition 
with pressure. The relation of vapor pres- 
sure to temperature has thus far defied the 
counsels of the wise, even though such men 
as Bertrand and Dupré have given the mat- 
ter close scrutiny. One would suspect the 
simplest relation to hold for metallic boil- 
ing points, and investigations have there- 
fore been undertaken in which the temper- 
ature of ebullition of Hg, Cd, Zn, Bi, were 
studied for pressures decreasing from one 
atmosphere down indefinitely. 
The results so obtained show an effect of 
pressure regularly more marked as the nor- 
mal boiling point is higher, so that the at- 
tempt to express the phenomenon for all 
these bodies by a common equation is 
roughly successful. By far the most rapid 
reduction of boiling point occurs when the 
pressure decreases from =, atmosphere in- 
definitely. For the case in which the nor- 
mal boiling point is to be predicted from a 
low pressure value in case of a metal which, 
like bismuth, boils with great difficulty, 
very high exhaustion is essential. 
Igneous fusion, by which I mean the fu- 
sion of rock-forming magmas, is particularly 
interesting in its relation to pressure. This 
has been again recently pointed out by 
Clarence King in his discussion of the age 
of the earth. If the earth is solid within, 
as is now generally admitted, such solidity 
can only result from superincumbent pres- 
sure withholding fusion. To study the re- 
lation of melting point to pressure directly 
is out of the question when white heat is 
the condition of fusion. In this respect 
the laboratory in the interior of the sun or 
even of the planets has some salient advan- 
tages, but we cannot comfortably put such 
a laboratory under strict surveillance of 
protoplasm. 
Fortunately, the Clapeyron equation, suc- 
cessively improved by James Thomson and 
