" continued the man of science too much bent on
his own ideas, to understand her interruption. "Little danger of that!
I made my own base, knew the length of the perpendicular by calculation,
and to draw the hypothenuse had nothing to do but to work my angle. I
supposed the guns were fired for my benefit, and changed my course
for the sounds--not that I think the sense more accurate, or even as
accurate as a mathematical calculation, but I feared that some of the
children might need my services."

"They are all happily--"

"Listen," interrupted the other, already forgetting his affected anxiety
for his patients, in the greater importance of the present subject. "I
had crossed a large tract of prairie--for sound is conveyed far where
there is little obstruction--when I heard the trampling of feet, as if
bisons were beating the earth. Then I caught a distant view of a herd
of quadrupeds, rushing up and down the swells--animals, which would
have still remained unknown and undescribed, had it not been for a most
felicitous accident! One, and he a noble specimen of the whole! was
running a little apart from the rest. The herd made an inclination in my
direction, in which the solitary animal coincided, and this brought
him within fifty yards of the spot where I stood. I profited by the
opportunity, and by the aid of steel and taper, I wrote his description
on the spot. I would have given a thousand dollars, Ellen, for a single
shot from the rifle of one of the boys!"

"You carry a pistol, Doctor, why didn't you use it?" said the half
inattentive girl, anxiously examining the prairie, but still lingering
where she stood, quite willing to be detained.

"Ay, but it carries nothing but the most minute particles of lead,
adapted to the destruction of the larger insects and reptiles. No, I did
better than to attempt waging a war, in which I could not be the
victor. I recorded the event; noting each particular with the precision
necessary to science. You shall hear, Ellen; for you are a good and
improving girl, and by retaining what you learn in this way, may yet be
of great service to learning, should any accident occur to me. Indeed,
my worthy Ellen, mine is a pursuit, which has its dangers as well as
that of the warrior. This very night," he continued, glancing his eye
behind him, "this awful night, has the principle of life, itself, been
in great danger of extinction!"

"By what?"

"By the monster I have discovered. It ap