long, and 5 inches (12.7 centimetres) wide, and has a hole, 31 inches (8.3 centimetres) in diameter, cut in the centre. The iron bolt and nut must go through the back of the box, and must have a washer wide enough to cover the slot in the slide. A few inches below the bolt a block of wood is fastened to the back of the box in the slot of the slide, to serve as a guide in raising and lowering the slide carrying the lens. In the hole in the shelf rests a large watchglass, or shallow dish, about 4 inches (10.1 centimetres) in diameter. The plano-convex lens used in our experiments in projection may be here used in place of the watch-glass. On each side of the shelf are two upright wooden arms, and between them is placed a looking-glass 7 inches (17.8 centimetres) long, and 4 inches (10.1 centimetres) wide. To hold this mirror in place, screws may be put through the top of uprights into the frame, so that it will hang suspended, and turn freely up or down.

This apparatus can be made for about $3.20, the woodwork costing $1, the two mirrors $1.50, the two lenses costing 70 cents; and when it is ready for work it will be a fine lantern suitable for projecting large pictures upon a screen. Place the lantern before the heliostat, so that the full beam of light will be reflected from the mirror upward through the glass

bowl and the watch-glass. Fill each of these with

the swinging mirror at Hang up a large screen

clear water, and then place the top at an angle of 45°. of white cotton cloth or sheet in front of the lantern, and from 15 to 40 feet (4.57 to 12.20 metres) from the lantern. On this screen will appear a circle of light projected from the lantern. The sunlight from the mirror is refracted in the large water-lens and brought to a focus. It is again refracted in the small glass of water, and is reflected by the mirror on the screen. Get a piece of smoked glass, and trace upon it some letters, and then lay it on the water-lens with the top (upper side of the writing) toward the screen: immediately the letters will appear on the screen, in white on a black ground. If the projection is not distinct, loosen the nut at the back of the box, and move the wooden slide up or down till the right focus is obtained.

This water-lantern may now be used for all the work performed with ordinary magic lanterns. Place a sheet of clear glass over the large lens to keep the dust out of the water, and then lay common lantern-slides on this as in a magic lantern.

The most simple slides for such a lantern can be made by laying thin paper over engravings or drawings, and tracing the picture with lines of holes

pricked with a pin. In the lantern such a paper slide will show the lines of the picture in dots of light on a dark ground. Another way is to write or draw on sheets of smoked glass. A curious effect may be made by placing the smoked glass in the lantern and writing upon it, upside down and backward, when the letters will appear to grow out in big white characters on the dark screen, and afford much amusement to all who see it. Of course, the film of smoke will easily rub off, and each scratch and finger-mark will be shown on the screen, and the work is often dirty and troublesome; but it has the advantage of being quickly done, and, if the picture is not right, it can be rubbed out and another put in its place.

A better kind of slide may be made by drawing with a needle on sheets of gelatine. Sheets of gelatine, 18 inches (45.7 centimetres) square, can be bought for 35 cents, either pure and transparent or in a variety of colors. Lay a piece of this on an engraving, and trace the picture, drawing, map, or outline, with the point of a large needle-do not press very hard on the gelatine; a mere scratch is enough-and in the lantern every line and dot will be visible, in black upon a white or colored ground. To preserve these sheets of gelatine, put them between sheets of glass, and bind them together with paper pasted over the edges.

Another kind of slide may be made by flowing skimmed milk over sheets of glass. When the white film of milk is dry, drawings may be traced in it with a sharp pencil or pointed stick. Another plan is to rub Castile soap over glass, and to draw on this in the same way. By this plan you can destroy the picture by rubbing on more soap, and you may then make a new picture in it.

This lantern is quite as good as the best magic lanterns. For schools, where one boy or girl wishes to show a sum in arithmetic, an example in algebra, a map, or sample of penmanship, to the whole school, the sun-lantern and piece of smoked glass, or a sheet of gelatine, will enable him to project it on a screen, so that a hundred boys and girls can see it

at once.

Another interesting experiment may be made with this lantern by taking the glass cover off of the large lens, and dropping a very small chip of wood in the water. It will be pictured in gigantic size upon the screen, and curious fringes of shade will gather round it, showing where the water clings to the wood. A drop of camphor or of oil of coriander or oil of cinnamon, let fall into the water, will exhibit geometrical figures and strange motions on the screen; and a few drops of indigo or carmine ink will color the

screen blue or red, and make an excellent background for some of the pictures.

To describe all that could be done with this waterlantern and heliostat would fill a book. Having made them, you can consult other books on making projections, and find the lantern a source of amusement and instruction for hundreds of people for a very long time.

THE SOLAR MICROSCOPE.

Fig. 25 represents a common round glass flask, about 6 inches (15.3 centimetres) in diameter; a common pocket-microscope lens of 1 inch focus (costing 25 cents), and a glass slide, carrying a microscopic object. The flask is filled with water, and is placed on a table just at the opening of the heliostat, so that the light will be refracted in it and brought to a focus. It is thus a water-lens, and may be used to bring a focus of light upon any object placed near it. Just behind this focus we place a glass slide, containing some object to be examined in a microscope. To hold this slide upright, we stick it in a mass of wax. The magnifying-glass is fastened to a bit of wax resting on a block of wood, so that it may be moved backward or forward along a strip nailed down on another block. About 15 feet (4.57 metres) from the