gh a prism. Either purchase one or
make it of three plain pieces of glass one and a half inch wide
by six inches long, fastened together in triangular shape--fasten
the edges with hot wax and fill it with water; then on a screen
or wall you will have the colors of the rainbow, not merely seven
but seventy, if your eyes are sharp enough.

Take a bit of red paper that matches the red color of the spectrum.
Move it along the line of colors toward the violet. In the orange
it is dark, in the yellow darker, in the green and all beyond,
black. That is because there are no more red rays to be reflected
by it. So a green object is true to its color only in the green
rays, and black elsewhere. All these colors may be recombined by
a second prism into white light.

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III.

ASTRONOMICAL INSTRUMENTS.

"The eyes of the Lord are in every place."--_Proverbs_ xv. 3.

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"Man, having one kind of an eye given him by his Maker, proceeds
to construct two other kinds. He makes one that magnifies invisible
objects thousands of times, so that a dull razor-edge appears as
thick as three fingers, until the amazing beauty of color and form
in infinitesimal objects is entrancingly apparent, and he knows that
God's care of least things is infinite. Then he makes the other kind
four or six feet in diameter, and penetrates the immensities of space
thousands of times beyond where his natural eye can pierce, until he
sees that God's immensities of worlds are infinite also."--BISHOP
FOSTER.

[Page 43]
III.

_THE TELESCOPE._

Frequent allusion has been made in the previous chapter to discovered
results. It is necessary to understand more clearly the process by
which such results have been obtained. Some astronomical instruments
are of the simplest character, some most delicate and complex.
When a man smokes a piece of glass, in order to see an eclipse
of the sun, he makes a simple instrument. Ferguson, lying on his
back and slipping beads on a string at a certain distance above
his eye, measured the relative distances of the stars. The use
of more complex instruments commenced when Galileo applied the
telescope to the heavens. He cannot be said to have invented the
telescope, but he certainly constructed his own without a pattern,
and used it to good purpose. It consists of a lens, O B (Fig. 13),
which acts as a multiple prism to bend all the rays to one point
at R. Place the eye there, and it receives as much