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. [Illustration: Scale of Butterfly MAGNIFIED 200 DIAMETERS.] [Illustration: HEAD OF MOSQUITO. MAGNIFIED 15 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. 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. [Illustration: 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 internal or cellular structure of the vegetable kingdom. IV.--HOME EXPERIMENTS. [Illustration: FIG. 1.]