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HOW DO MICROSCOPES WORK?

Microscopes have at least two curved lenses that work together. Examine them carefully.

The lens nearest the object being viewed is the objective lens. The lens nearest the viewer's eye is the eyepiece.

Locate the platform, or "stage" beneath the objective lens. The clips hold glass slides on the platform. Beneath the platform is a mirror that can be turned to reflect light
from a lamp or window onto the viewed object. (CAUTION: Never turn the mirror directly toward the sun.)

The mirror can be adjusted until a uniform circle of light without shadows is seen. This circle is called a "field."

Place a small drop of water in the center of a clean, dry, glass slide. Cut a small letter "e" from a newspaper and lay it right-side up in the drop of water. Slowly place the
cover glass over the water by placing one edge down first (to prevent air bubbles from being caught between the glasses.)

Now place the mounted slide onto the platform, clip it into place, and move it with thumbs and forefingers until the letter "e" is in the center of the platform opening. Turn
the coarse adjustment knob to move the objective lens down as far as it will go, but be careful not to touch the slide. (Look at the slide from the side to be sure the objective lens does not touch or break the slide.)

Take turns looking through the eyepiece, watching the field as you turn the coarse adjustment knob slowly toward yourself. This will raise the body of the tube and the
lenses, and you will see the letter "e" appear. The adjustment can be moved slowly up and down to focus the letter. Move the slide to the right, left, up, and down.

You will find that everything seen through the eyepiece is reversed. You may be interested in looking up the work of Anton von Leeuwenhoek (1632-1723), a Dutch merchant and amateur scientist -- the first person to perfect the microscope.

List some things you can see with a microscope that you cannot see with your "naked" eyes.

Here are some more fun things to do with a microscope:

Place a culture or specimen in the center of a clean, dry glass slide. If the specimen is liquid, a cover glass can be placed over the top by placing one edge down first to prevent bubbles from becoming trapped beneath the glass.

If the water begins to dry up while you are viewing, use a medicine dropper to place a little more water along the edge of the cover glass. Bacterial cultures can be fixed to slides by spreading a drop so that it forms a thin film on the glass. Allow it to dry, then pass it through a flame (ADULT SUPERVISION REQUIRED HERE!) three or four times to kill the culture and fix it to the slide.

Now put several drops of methylene-blue stain on the culture to improve viewing. Leave it for two minutes, then dip the slide in water to wash off excess stain. Blot gently with a paper towel and view under a microscope.

Sometimes it is best not to press the object being viewed with the cover glass. Special slides with indentations in them can be purchased, or the cover glass can be raised by making a ring of petroleum jelly slightly smaller than the cover on the slide. Place a drop of a culture in the ring and add the cover glass.

An alternative method is to break a cover glass into several pieces, place the pieces on a slide, cover them with an unbroken cover glass, and then glue the pieces in place. A culture can be dropped between the slide and the raised cover.

 
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