ave mirror forms an image of the
burning candle.]

HOW THE MICROSCOPE WORKS. But the microscope is different. It works
like this: The first lens is put very near the object which you are
examining. This lens brings the light from the object to a focus and
forms an image, much larger than the object itself, high up in the
tube. If you held a piece of paper there you would see the image.
But since there is nothing there to stop the light, it goes on up the
tube, spreading as it goes. Then there is another lens which catches
this light and bends it inward on its way to your eye, just as any
magnifying glass does. Next the lens in the eye forms an image on
the retina. The diagram (Fig. 84) will make this clearer. (A real
microscope is not so simple, of course, and usually has two lenses
wherever the diagram shows one.) What actually happens is that the
first lens makes an image many times as big as the object; then you
look at this image through a magnifying glass, so that the object is
made to look very much larger than it really is. That is why you can
see blood corpuscles and germs and cells through a microscope, when
you cannot see them at all with your naked eye.

[Illustration: FIG. 87. The great telescope of the Yerkes Observatory
at Lake Geneva, Wisconsin.]

A MIRROR THAT MAGNIFIES. A convex lens is not the only thing that can
magnify. A concave mirror, which is one that is hollowed out toward
the middle, does the same thing. When light is reflected by such a
mirror, it acts exactly as if it had gone through a convex lens (Fig.
85).

EXPERIMENT 49. Place the lighted candle and the paper about 4
feet apart, as you did in Experiment 47. Hold a concave mirror
_back_ of the candle (so that the candle is between the mirror
and the paper); then move the mirror back, the mirror casting
the reflection of the candle light on the paper, until a clear
image of the candle is formed.

Look at your image in the concave mirror. Does it look larger
or smaller than you?

HOW TELESCOPES ARE MADE. Astronomers use convex lenses in some of
their telescopes; in others, called _reflecting telescopes_, they use
concave mirrors. Both do the same work, making the moon, the planets,
and the sun look much larger than they otherwise would.

_APPLICATION 37._ Explain how a reading glass makes print look
larger; how you can see germs through a microscope; what kind
of mirror will magnify; what