res far below their fusion
point, still retain a very appreciable conductivity, become, on the
contrary, perfect insulators at low temperatures. Their dielectric
constants assume relatively high values. MM. Curie and Compan, who
have studied this question from their own point of view, have noted,
moreover, that the specific inductive capacity changes considerably
with the temperature.

In the same way, magnetic properties have been studied. A very
interesting result is that found in oxygen: the magnetic
susceptibility of this body increases at the moment of liquefaction.
Nevertheless, this increase, which is enormous (since the
susceptibility becomes sixteen hundred times greater than it was at
first), if we take it in connection with equal volumes, is much less
considerable if taken in equal masses. It must be concluded from this
fact that the magnetic properties apparently do not belong to the
molecules themselves, but depend on their state of aggregation.

The mechanical properties of bodies also undergo important
modifications. In general, their cohesion is greatly increased, and
the dilatation produced by slight changes of temperature is
considerable. Sir James Dewar has effected careful measurements of the
dilatation of certain bodies at low temperatures: for example, of ice.
Changes in colour occur, and vermilion and iodide of mercury pass into
pale orange. Phosphorescence becomes more intense, and most bodies of
complex structure--milk, eggs, feathers, cotton, and flowers--become
phosphorescent. The same is the case with certain simple bodies, such
as oxygen, which is transformed into ozone and emits a white light in
the process.

Chemical affinity is almost put an end to; phosphorus and potassium
remain inert in liquid oxygen. It should, however, be noted, and this
remark has doubtless some interest for the theories of photographic
action, that photographic substances retain, even at the temperature
of liquid hydrogen, a very considerable part of their sensitiveness to
light.

Sir James Dewar has made some important applications of low
temperatures in chemical analysis; he also utilizes them to create a
vacuum. His researches have, in fact, proved that the pressure of air
congealed by liquid hydrogen cannot exceed the millionth of an
atmosphere. We have, then, in this process, an original and rapid
means of creating an excellent vacuum in apparatus of very different
kinds--a means which, in certain cases,