actly overhead, and its
rays came nearly straight down. If I had had a glass rounded out on both
sides I could have got fire any time after the sun was well up in the
sky. Now let me tell you what they call all these different kinds of
glasses. One that is flat on one side and bulges out on the other is
called a _convex lens_; if it bulges out on both sides it is a _double
convex lens_; if it is hollowed in on one side and flat on the other it
is a _concave lens_; if hollowed in on both sides we call it a _double
concave lens_; and when it is hollowed in on one side and bulged out on
the other, as any watch crystal does, it is a _concave convex lens_."

"Where did you learn all that, Sam?" asked Tom.

"I learned part of it with father's spectacles, and part out of a book
father lent me when I asked him why I couldn't make the bright, hot spot
with a pair of near-sighted glasses that I found in one of mother's old
work boxes. You see, when people begin to get old, their eyes flatten a
little, and so everything they look at seems to be shaved off. They see
well enough at a distance, but can't see small things close to them."

"Is that the reason pa always looks over his spectacles when he looks at
me?" asked Judie.

"Yes, little woman. He can't see to read without his glasses, but he
can see you across the room without them, well enough. Well, to remedy
this defect, old people wear spectacles with double convex lenses in
them. But near-sighted people have exactly the opposite trouble. They
can't see things except by bringing them near their eyes, because their
eyes are not flat enough, and so their spectacles are made with double
concave lenses. When I asked father about it, he gave me a book that
explained it all, and that is where I learned the little I know about
it."

"The _little_! I'd like to know what you call a good deal," said Tom. "I
never saw anybody that knew half as much as you do."

"That is only because we live in a new country, Tom, where there are no
very well educated people, and because you don't know how much there is
to learn in the world. If these Indians ever get quiet, I hope to learn
a good deal more every year than I know now. But it's time to see about
our mussel bake. Run to the look-out, Tom, and then we can all go down
and bring up the dinner."

CHAPTER VI.

SURPRISED.

The baked corn and mussels made a savory dish, or one which would have
been savory enough but for the abs