Fig. 4. An ingenious boy with a block of wood for a base, some stout wire and corks, can make one almost as useful, though not so handsome.

FIG. 6

A more elaborate form is shown in Fig. 5. It has a glass stage to hold transparent objects, and a brass one for opaque objects, and a mirror below to reflect light up through transparent objects.

It is much better to use a good simple microscope than a poor and cheap compound one; be sure and remember this and not be enticed to buy such an one by any representations as to its great magnifying power.

A compound microscope is one with a tube from four to ten inches long, an arrangement for holding the object to be looked at, and a mirror below to reflect light upon or through it. The lenses at the end next the object are small, and are set in a small brass tube, which is called an "objective." It screws into the large tube. The lenses at the end of the large tube next the eye are set in a tube, called the eye-piece, which slides in and out of the large tube. Different objectives contain lenses of different sizes according to the magnifying power desired, and they are named "two inch," "one inch," "half inch," and so on down to "one seventy-fifth." Eye-pieces are sometimes named "A," "B," "C," but more properly "two inch," and so on down to "one eighth." There is a very great variety in the forms of compound microscopes, from the very simple up to the very elaborate, and the prices vary accordingly. A simple but useful form is given in Fig. 6.

CATCHING ANIMALCULA WITH A PIPETTE.

A great deal of money can be expended on a microscope and the various instruments made to use with it and which are called "accessory apparatus"; but it is best not to buy these instruments until you know just what you want, and not to spend much money at first except under the advice of a "microscopist."

Some simple things, however, you will need at once, such as a few slips of glass three inches long and one inch wide, called "glass slides," some pieces of very thin glass, called "cover glass," a pair of tweezers, some needles fastened into pen-holders for handles, and a few glass tubes commonly called "pipettes," or "dipping tubes." These can be readily bought, and some of them easily made.

III.—OBJECTS.

As soon as you have a microscope you will begin to look at everything and anything: dust, crumbs of bread, flour, starch, mosquitoes, flies, and moth millers in their season; flowers and leaves, cotton, wool, and silk. But this scattering kind of observation will soon weary you. In order to get the greatest pleasure and best results from your work, you must proceed with some system.

BULL'S EYE LENS.

MAGNIFIED 50 DIAMETERS.

There are so many objects visible only through the microscope that life is not long enough for you to see them all, much less to study them. Some microscopists devote the time they have for such studies to the observation of single classes of objects; the physician observes the various parts of the animal structure, and calls his work "histology;" the botanist examines the vegetable kingdom; the entomologist, insects; but in all these departments there are numerous subdivisions. As a guide to your work, you will find some book on the microscope very useful; the best one is The Microscope and its Revelations, by Dr. William B. Carpenter.

FLY'S EYE—5 DIAMETERS.

Objects through which you can see light are called "transparent," and are the easiest to look at with the microscope, because you can lay them on a glass slide and throw light up through them with your mirror. Thick objects through which light cannot pass are called "opaque," and are more difficult to examine, and can only be seen with low powers and a bright light.

In order to see such objects in the evening, you will need a "bull's eye" lens mounted on a stand, which you can place beside your microscope and between the lamp and the stage, condensing the light of the lamp on the object. (Fig. 1.) There are other methods of illuminating opaque objects, but they are expensive and difficult to manage, yet by and by if you persevere in this delightful occupation you will learn what they are.

MAGNIFIED 200 DIAMETERS.

Some persons will expect you to show them a fly as big as a horse; but you will soon be able to prove to them that you know more about the matter than they do. With a large hand-lens, you can see a whole fly at once and magnify it two or three times; but when you put it on the stage of your compound microscope and try to magnify it still more, you will find that you can only see a part of it at a time, and the higher the power you use, the less can you see; in other words, the more you magnify an object, the smaller is the field of view.

HEAD OF MOSQUITO. MAGNIFIED 15 DIAMETERS.

An inch-objective will show the head of an housefly, which in a bright light is a very beautiful object. No picture can equal the delicacy of the color of the eyes of a live fly.

SECTION OF WOOD.
MAGNIFIED 50 DIAMETERS.

After a little practise you will be able to separate the different parts of insects and look at them with higher powers. The moth fly will soon be on the wing, and your aunt will not call you cruel if you kill and cut up large numbers of them. Put a little of the dust that comes off from the wing of a moth on a glass slide, look at it with a high power, and you will find that each particle of dust is a pretty leaf-like scale. You have seen in summer the dust on the wings of butterflies; remember this, and look at this butterfly dust with your microscope.

Flowers and leaves you can always easily obtain; but in looking at them you must remember what has already been said about "transparent" and "opaque" objects.

Thin slices or sections of stems, leaves, and portions of flowers, can be made with a sharp knife, and examined as transparent objects, so that thus you can observe the