erally 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,
holding it far from his body, as he tip-toed up to the platform, where
he laid it down carefully on the desk before the Professor.

"Thank you," said the Professor, blandly.

The man drew a long breath of relief as he went back to his seat.

"That is frozen dynamite," continued the Professor, "and is, as I have
said, practically harmless. Now, it will be my pleasure to perform two
startling experiments with the unfrozen substance," and with that he
picked up a handful of the wet sawdust and flung it on a small iron
anvil that stood on the table. "You will enjoy these experiments," he
said, "because it will show you with what ease dynamite may be handled.
It is a popular error that concussion will cause dynamite to explode.
There is enough dynamite here to blow up this hall and to send into
oblivion every person in it, yet you will see whether or not concussion
will explode it." The Professor seized a hammer and struck the
substance on the anvil two or three sharp blows, while those in front
of him scrambled wildly back over their comrades, with hair standing on
end. The Professor ceased his pounding and gazed reproachfully at them;
then something on the anvil appeared to catch his eye. He bent over it
and looked critically on the surface of the iron. Drawing himself up to
his full height again, he said,

"I was about to reproach you for what might have appeared to any other
man as evidence of fear, but I see my mistake. I came very near making
a disastrous error. I have myself suffered from time to time from
similar errors. I notice upon the anvil a small spot of grease; if my
hammer had happened to strike that spot you would all now be writhing
in your death-agonies under the ruins of this building. Nevertheless,
the lesson is not without its value. That spot of grease is free nitro-
glycerine that has oozed out from the dynamite. Therein rests, perhaps,
the only danger in handling dynamite. As I have shown you, you can
smash up dynamite on an anvil without danger, but if a hammer happened
to strike a spot of free nitroglycerine it would explode in a moment. I
beg to apologize to you for my momentary neglect."

A man rose up in the middle of the hall, and it w