us, he was a mystery, for the
reason that he seemed to be at home in every direction where it called
for any special activity. This was made the more mystifying when, during
the next day, he wandered over to the laboratory, and his eyes caught
sight of the skulls and the skeletons which were on exhibition.

He walked over to the skulls, and picking up one poised it on his hand,
slowly turning it around, as though trying to discover what it meant.
The one selected had one side partially crushed, and this attracted his
attention. He placed the fingers of the other hand in the shattered
part, and seemed to realize that some agency must have caused it. The
whole deportment while examining it was that of one who was called upon
to make an examination of it for the purpose of determining the cause of
the injury.

When he laid it down, he looked at the Professor, who quietly took up
the skull and pointed to the fracture, endeavoring by his conversation
to strike a word or keynote by which some recollection would be started;
but he was mute and soon again became listless.

CHAPTER XIV

AN EXCITING TRIP TO THE FALLS

The food supply was now the first thing to consider, as all necessaries
in the way of vegetables, as well as meats, had been exhausted when they
started on the last trip, and a new lot had to be laid in. The matter of
butter was always a hard problem to take care of, and George referred to
this difficulty, and before they sailed away the Professor told him
that, on their return, the first thing to do would be the construction
of a machine which would simplify the production of the butter.

"As we are going to use more butter, I think it would be a good thing to
start in on our cream separator," said George, who, while he was not an
adept, like Harry, to devise the things required, was always ready to
suggest things that could be made to advantage.

"I know that Harry will be very glad to set to work on that, so we might
as well commence," answered the Professor.

"What is the principle of the separator that causes the cream to break
away from the milk?"

"Centrifugal motion is employed to bring it about."

"But how does that motion affect it?"

"When you put a ball on an elastic and swing it about your head in a
circle, the elastic stretches in proportion to the speed at which you
swing it. You have probably seen it done. It is stretched in proportion
to its weight, also. These two things, there