e
quantities for mining purposes. Here is some of it," I added, pulling
from my pocket a cartridge nearly two inches in length, and about an
inch in diameter. "It is a soft, pasty substance, done up, as you see,
in cartridge-paper, and this little thing, if properly fired, would blow
a large boulder-stone to atoms."

"Bless me, boy, be careful!" exclaimed my mother, pushing back her chair
in some alarm.

"There is no danger," I said, in reassuring tones, "for this cartridge,
if opened out and set on fire by a spark or flame, would not, in the
first place, light readily, and, in the second place, it would merely
burn without exploding; but if I were to put a detonator inside and fire
it by means of _that_, it would explode with a violence that far exceeds
the force of gunpowder."

"And what is this wonderful detonator, Jeff, that so excites the latent
fury of the dynamite?"

I was much amused by the pat way in which my mother questioned me, and
became more interested as I continued my explanation.

"You must know," I said, "that many powders are violently explosive, and
some more so than others. This violence of explosion is called
detonation, by which is meant the almost instantaneous conversion of the
ultimate molecules of an explosive compound (i.e. the whole concern)
into gas."

"I see; you mean that it goes off quickly," said my mother, in a simple
way that was eminently characteristic.

"Well, yes; but much more quickly than gunpowder does. It were better
to say that a powder detonates when it _all_ explodes at the _same_
instant. Gunpowder appears to do so, but in reality it does not. One
of the best detonators is fulminate of mercury. Detonating caps are
therefore made of this, and one such cap put into the middle of that
cartridge of dynamite and set fire to, by any means, would convert the
cartridge itself into a detonator, and explode it with a _shattering_
effect.

"A human being," I continued, "sometimes illustrates this principle
figuratively--I mean the violent explosion of a large cartridge by means
of a small detonator. Take, for example, a schoolmaster, and suppose
him to be a dynamite cartridge. His heart is a detonating cap. The
schoolroom and boys form a galvanic battery. His brain may be likened
to a conducting-wire. He enters the schoolroom; the chemical elements
are seething in riot, books are being torn and thrown, ink spilt,
etcetera. Before opening the door, the good man