e than the recorded tricks of dogs and many
other animals?

You know just how boys can laugh when they are really happy. Angel
imitated that laugh, and he had not been taught to do it, either. It
came without teaching.

When the Professor had wiped away some of the tears which had come from
the excess of laughter at the imitating efforts of the animal, he said:

"Did it ever occur to you why Angel has always had a solemn look? The
facial expression seldom, if ever, changes, and they rarely ever exhibit
mirth. You may imagine the condition of those animals, living in the
forests, with enemies all about them, and the struggle for existence an
everlasting one. They have never known amusing incidents as we
understand them. Naturally, the muscles of mobility in the face, which
express pleasure, never have been exercised, and those indicating fear
and anger unduly developed. Here is Angel, in a new atmosphere, where he
sees delight depicted on the countenance, and, gifted as he is, with
wonderful powers of imitation, has learned to actually laugh, and to
enjoy the scene."

"Well, Professor, as we have one of the guns polished up and completed,
wouldn't it be well to make the bullets?"

"For that purpose I suggest that we make the molds out of a metal or
alloy which has a higher fusing point than lead."

"What is best for the purpose?"

"We might make an alloy of copper and zinc."

"Oh! You mean brass?"

"Yes; that is readily cast and easily worked."

"But what shape shall we make the bullets?"

"They should be made long, with a pointed forward end."

"Why is a long bullet better than a round or globe-shaped ball?"

"There are several very important reasons. First, momentum is a prime
element in a missile. A long one contains double the metal of a
spherical one. Second, it can be made so that it will expand when the
explosion of the powder takes place."

"In what way does it expand?"

"You have noticed that the rear end of the bullet has a cavity. When the
explosion takes place the thin shell at the rear end of the bullet
expands, so that it tightly hugs the bore of the gun."

"What is the object of having it do that?"

"To give the ball the benefit of the charge of powder exploded. If it
does not fit tightly in the bore, more or less of the powder will pass
the ball, and thus the ball loses part of its force."

"What is the object of rifling the gun?"

"The object is to impart to the bullet a spiral mo