only one inch, or about as large as a plum or a
half-grown peach; then we would have to regard the sun as three yards in
diameter, so that if it were in this room it would reach from the floor
to the ceiling."

"How do they find out the distance of the sun?" asked Joe.

"Until lately," replied the Professor, "the same method was pursued as
in surveying, that is, by measuring lines and angles. An angle, you
know, is the corner made by two lines coming together, as in the letter
V. But that method did not answer very well, as it did not make the
distance certain within several millions of miles. Quite recently
Professor Newcomb has found out a way of measuring the sun's distance by
the velocity of its light. He has invented a means of learning exactly
how fast light moves; and then, by comparing this with the time light
takes to come from the sun to us, he is able to tell how far off the sun
is. Thus, if a man knows how many miles he walks in an hour, and how
many hours it takes him to walk to a certain place, he can very easily
figure up the number of miles it is away."

"Why," said Gus, "that sounds just like what Bob Stebbins said the other
day in school. He has a big silver watch that he is mighty fond of
hauling out of his pocket before everybody. A caterpillar came crawling
through the door, and went right toward the teacher's desk at the other
end of the room. 'Now,' said Bob, 'if that fellow will only keep
straight ahead, I can tell how long the room is.' So out came the watch,
and Bob wrote down the time and how many inches the caterpillar
travelled in a minute. But just then Sally Smith came across his track
with her long dress, and swept him to Jericho. We boys all laughed out;
Sally blushed and got angry; and the teacher kept us in after school."

"Astronomers have the same kind of troubles," said the Professor. "They
incur great labor and expense to take some particular observation that
is possible only once in a number of years, and then for only a few
minutes. And after their instruments are all carefully set up, and their
calculations made, the clouds spread over the sky, and hide everything
they wish to see. People, too, are very apt to laugh at their
disappointment.

"There would, however, be no science of astronomy if those who pursued
it were discouraged by common difficulties. To explain the heavenly
bodies they sometimes try to make little systems or images of the sun
and the planets; but they a