"Yet," continued the Professor, "it will be useful for us to consider
this substance for a few moments, if but for the purpose of comparison.
Here," he said, diving his hand into another box and bringing up before
their gaze a yellow brick, "is dynamite in a compressed form. There is
enough here to wreck all this part of London, were it exploded. This
simple brick would lay St. Paul's Cathedral in ruins, so, however
antiquated dynamite may become, we must always look upon it with
respect, just as we look upon reformers of centuries ago who perished
for their opinions, even though their opinions were far behind what
ours are now. I shall take the liberty of performing some experiments
with this block of dynamite." Saying which the Professor, with his free
arm, flung the block of dynamite far down the aisle, where it fell on
the floor with a sickening thud. The audience sprang from their seats
and tumbled back one over the other. A wild shriek went up into the
air, but the Professor gazed placidly on the troubled mob below him
with a superior smile on his face. "I beg you to seat yourselves," he
said, "and for reasons which I have already explained, I trust that you
will not applaud any of my remarks. You have just now portrayed one of
the popular superstitions about dynamite, and you show by your actions
how necessary a lecture of this sort is in order that you may
comprehend thoroughly the substance with which you have to deal. That
brick is perfectly harmless, because it is frozen. Dynamite in its
frozen state will not explode--a fact well understood by miners and all
those who have to work with it, and who, as a rule, generally prefer to
blow themselves to pieces trying to thaw the substance before a fire.
Will you kindly bring that brick back to me, before it thaws out in the
heated atmosphere of this room?"

One of the men stepped gingerly forward and picked up the brick,