f the air suffer a like fate. The
responsible substance which plays the part of the familiar mercury, or
alcohol, in Dr. Travers's marvellous thermometer is hydrogen gas.
The principle by which it is utilized does not differ, in its rough
essentials, from that of ordinary thermometers, but the details of its
construction are much too intricate to be elaborated here.

But if you would see the most wonderful things in this laboratory--or
rather, to be quite accurate, I should say, if you would stand in the
presence of the most wonderful things--you must go with Professor
Ramsay to his own private laboratory, and be introduced to some little
test-tubes that stand inverted in cups of mercury decorating a shelf at
one end. You would never notice these tubes of your own accord were
you to browse ever so long about the room. Even when your attention
is called to them you still see nothing remarkable. These are ordinary
test-tubes inverted over ordinary mercury. They contain something, since
the mercury does not rise in them completely, but if that something be
other than ordinary air there is nothing about its appearance, or rather
lack of appearance, to demonstrate it. But your interest will hardly
fail to be arrested when Professor Ramsay, indicating one and another of
these little tubes, says: "Here you see, or fail to see, all the krypton
that has ever been in isolated existence in the world, and here all the
neon, and here, again, all the zenon."

You will understand, of course, that krypton, neon, and zenon are the
new gases of the atmosphere whose existence no one suspected until
Professor Ramsay ferreted them out a few years ago and isolated them. In
one sense there should be nothing mysterious about substances that every
air-breathing creature on the globe has been imbibing pretty constantly
ever since lungs came into fashion. But in another view the universal
presence of these gases in the air makes it seem all the more wonderful
that they could so long have evaded detection, considering that
chemistry has been a precise science for more than a century. During
that time thousands of chemists have made millions of experiments in the
very midst of these atmospheric gases, yet not one of the experimenters,
until recently, suspected their existence. This proves that these gases
are no ordinary substances--common though they be. Personally I have
examined many scientific exhibits in many lands, but nowhere have I seen
an