ting again; but they did not succeed in ascertaining
whether the short one went more or less than twice as fast as the other.
The two motions, so rapid and so near together, confused them. At
length, Mary proposed that Rollo should count the vibrations of the long
pendulum, while she counted those of the short one, and when she had got
up to twenty, she said they would both stop, and then Rollo could tell
how many he had got in the same time. But this plan, though apparently a
very simple one, they found it somewhat difficult to put into practice.
Mary's pendulum puzzled Rollo's counting, and Rollo, who could not count
very well without at least whispering the numbers, puzzled Mary, and so
pretty soon they gave it up.

Rollo then said that he meant to try a very short pendulum indeed, and
he asked Mary to tie one up for him, not more than an inch in length.
She, however, said that it would not be necessary to tie it to the
branch; but, instead of that, she took hold of the string of one of the
pebbles which was already hanging before them, about an inch above the
pebble itself, and then set the pebble in motion; and they were both
very much interested in observing how quick it vibrated to and fro.

Rollo then wanted to try a very long one, and proposed that he should
climb up into the tree, and tie the end of the string to a high branch.
But Mary was afraid that he would fall; and besides, she said that the
pendulum would not swing clear of the branches below. She, however,
immediately thought of the chamber window, and said that she would try
it there. She accordingly went up into her chamber, taking a large
pebble stone with her, and Rollo remained below to set the pendulum in
motion, when it should be ready. Mary soon appeared at the window, and
Rollo watched her while she tied her pebble to the end of a thread.

"Have you got your thread long enough?" said Rollo. "It will take a
good long thread to reach away down here."

"It is a whole spool of cotton," said Mary. And, so saying, she held up
in her hand the spool, to the thread of which she was tying her pebble
stone.

When it was secured, she slowly let it down, until it reached Rollo's
hand, which was held up from below, ready to receive it. Mary then held
the thread steady above, at a little distance out from the window, while
Rollo took the stone along the side of the house, three or four feet
from the place where it would naturally hang. He then let it go,