ose
to where we look in, within an inch or so of our eye."

"A tiny image, uncle?"

"Well, picture, then."

"But you say tiny! It looks big enough when we put our eye to the
little round hole."

"To be sure it does. But what do you look through?"

"The eye-piece."

"Well, what is the eye-piece?"

"A little glass or two--lenses."

"These glasses or lenses form a microscope, Tom; and through them you
look at the tiny image formed in the focus of the great lens or the
speculum, whichever you use."

"But I thought microscopes were only used to magnify things invisible to
the eye."

"Well, Jupiter's moons, Saturn's ring, and the markings on Mars are all
invisible to the naked eye. So are the craters in the moon; so we use
the big speculum to gather the light, and then look at the spot where
all the rays of light come to their narrowest point, with an eye-piece
which really is a microscope."

"But I don't understand now," said Tom uneasily. "I wish I was not
so--"

"If you say stupid again, Tom, I shall quarrel with you," said Uncle
Richard sternly. "I never think any boy is stupid who tries to master a
subject. One boy's brain may be slower at acquiring knowledge than
another, but that does not prove him to be stupid. What is it you don't
follow?"

"About our telescope. If the light from the big speculum is all
reflected nearly to a point, ought we not to look down at it?"

"No; because then our heads would be in the way, and would cast a shadow
upon it. To avoid that, I put the little mirror in the middle, near the
top, just at the right slant, so that the rays are turned off at right
angles into the eye-piece, and so we are able to look without
interrupting the light."

"Oh, I see now," said Tom thoughtfully. "It's very clear."

"Yes," said Uncle Richard. "Sir Isaac Newton, who contrived that way,
was a clever man. Now then, let's get on with our work."

"I suppose then now we're ready?" said Tom.

"Far from it," replied his uncle; "are you going to hold up a
twelve-foot tube to your eye, and direct it to a star? The next thing
is of course to mount it upon trunnions, and arrange that it shall turn
upon an axis, so that we can sweep in any direction."

The longest tasks come to an end. By the help of the village carpenter,
a strong rough stand was connected with the beam formerly used to bear
the sails of the mill, the trunnions were fitted to a strong iron ring
by the smith, and on