ty of liquefied gas which would
evaporate in one minute from an ordinary vessel will last half an hour
in one of Professor Dewar's best vacuum vessels. Thus in one of these
vessels a quantity of liquefied air, for example, can be kept for a
considerable time in an atmosphere at ordinary temperature, and will
only volatilize at the surface, like water under the same conditions,
though of course more rapidly; whereas the same liquid in an ordinary
vessel would boil briskly away, like water over a fire. Only, be it
remembered, the air in "boiling" is at a temperature of about one
hundred and eighty degrees below zero, so that it would instantly freeze
almost any substance placed into it. A portion of alcohol poured on its
surface will be changed quickly into a globule of ice, which will
rattle about the sides of the vessel like a marble. That is not what one
ordinarily thinks of as a "boiling" temperature.

If the vacuum vessel containing a liquefied gas be kept in a cold
medium, and particularly if two vacuum tubes be placed together, so that
no exposed surface of liquid remains, a portion of liquefied air, for
example, may be kept almost indefinitely. Thus it becomes possible
to utilize the liquefied gas for experimental investigation of the
properties of matter at low temperatures that otherwise would be quite
impracticable. Great numbers of such experiments have been performed in
the past decade or so by all the workers with low temperatures already
mentioned, and by various others, including, fittingly enough, the
holder of the Rumford professorship of experimental physics at Harvard,
Professor Trowbridge. The work of Professor Dewar has perhaps been the
most comprehensive and varied, but the researches of Pictet, Wroblewski,
and Olzewski have also been important, and it is not always possible
to apportion credit for the various discoveries accurately, since
the authorities themselves are in unfortunate disagreement in several
questions of priority. But in any event, such questions of exact
priority have no great interest for any one but the persons directly
involved. We may quite disregard them here, confining attention to the
results themselves, which are full of interest.

The questions investigated have to do with the physical properties,
such as electrical conductivity, magnetic condition, light-absorption,
cohesion, and chemical affinities of matter at excessively low
temperatures. It is found that in all these