346 
by Clausius, is here usefully available. To 
measure the melting point, the difference 
of specific volumes of the solid and the 
liquid body and the latent heat of fusion 
at this temperature, with the aid of Joule’s 
equivalent, is to measure also the relation 
of melting point to pressure implicitly. 
Based on the first and second laws of ther- 
modynamics, this equation is generally true, 
no matter what specific properties may 
characterize the body. ‘The process has 
thus far been completely pushed through 
for diabase only. Thermal change of vol- 
ume may be measured by enclosing the 
rock ina platinum tube of known expan- 
sion, and the contraction of the contents 
from liquid to solid found by an electric 
micrometer probe reaching within the tube. 
Given a furnace fully under control, then, 
as experiment has shown, the cooling can 
be made to take place so slowly that plati- 
num remains rigid relatively to its charge 
of red-hot magma, and under these condi- 
tions the contraction can actually be fol- 
lowed into the solid state. At the same 
time the temperature at which marked 
change of volume occurs is the melting 
point. Apart from difficulties of manipu- 
lation, the latent heat may be found from 
measurement of thermal capacity on either 
side of the temperature of fusion by a 
modification of known methods. 
The rate at which fusion is retarded by 
pressure computed from these data in the 
manner specified showed an increase of the 
melting point of a silicate of about 0.025°C. 
per superincumbent atmosphere. But this 
datum falls within the margin (.02....04) 
of corresponding data much more easily 
and directly derived for organic bodies. 
One may, therefore, argue that if the melt- 
ing point pressure rate is so nearly constant 
on passing from the class of silicious to the 
thoroughly different and much more com- 
pressible class of organic bodies the rate 
would probably be more nearly constant 
SCIENCE. 
[N. 8. Vou. VI. No. 140. 
in the same body (silicious or organic), 
changed only as to temperature and pres- 
sure. This surmise was verified for naph- 
thalene within an interval of 2,000 atmos- 
pheres. 
The endeavor to interpret the change 
during fusion of the volume of the chem- 
ical elements in terms of the periodic system 
has been begun with much success by Max 
Tépler for low temperatures. It would be 
of great interest to complete this diagram 
for high temperatures in view of the spe- 
cifically molecular character of the fusion 
phenomenon, by repeating such experiments 
as have just been described for rock mag- 
mas. 
The heat conduction of rocks has been 
investigated in many cases for temperatures 
lying below red heat. Among recent ob- 
servers we need only instance the extensive 
investigations of Ayrton and Perry. No 
trustworthy experiments, however, have 
yet been carried into the region of essen- 
tially high temperature; and yet what is 
chiefly of interest in the geological applica- 
tions of such experiments is the change of 
conduction which accompanies changes of 
physical state, whether induced by pressure 
or by temperature. 
Experiments in heat conduction are diffi- 
cult under any circumstances. They be- 
come insuperably so when conduction at 
white heat is to be studied under pressure, 
and that is what the geological conditions 
actually imply. Some notion of a body re- 
spectively solid and liquid at a given tem- 
perature may be obtained by observing the 
behavior of bodies which are capable of 
being undercooled. A number of such 
bodies are known, thymol being a conspic- 
uous example. Experiments with this 
body were made by measuring the volume 
expansion, specific heat and heat conduc- 
tion in parallel series both for the solid and 
liquid state at like temperatures. They 
showed, for instance, that the increment of 
