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inserted in this hole, and by twirling the tube in the fingers the hole in the glass is made. The tube may also be put in a lathe. In the picture the flask stands upon a shelf in front of the heliostat, and

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just beneath it on the floor is placed a tub or a water-pail. These few things and some pieces of colored glass will enable us to perform a most inter

esting and beautiful experiment both in refraction and reflection. Place the finger over the hole in the side of the flask and fill it with water. Place the flask on the shelf so that the beam of light from the heliostat will strike the glass opposite the hole in the side.

Look at the beautiful cone of light in the water. The beam of light is refracted and brought to a focus as in our other experiments, except that here the cone is entirely under water. Study this singular cone carefully, and adjust the flask so that the point of the cone shines on the finger at the hole in the side. When this is done, make the room as dark as possible, and then remove the finger and let the water fall in a stream into the tub on the floor.

How magical! The curving stream of water is full of light, and appears like a stream of molten iron. The spot where it falls seems touched with fire. Put your finger in the stream of water, and it is brightly illuminated. Of course, the water soon runs down, and the display stops. To prevent this, bring water in a rubber tube from the water-pipes in the house, and then regulate the supply so that the receiver may be kept full as fast as the water runs out. Place a piece of red glass behind the flask in the beam of sunlight, and the stream of water will

look like blood. Touch it, and the hand will be crimson, and the scattered drops that fall in a shower into the tub will shine like drops of red fire. Place a green or blue glass behind the flask, and the stream of water will turn green or blue, and present a most singular appearance. Hold a goblet in the stream," and it will overflow with liquid light. Flashes and sparkles of fire will appear in it, and foam over the sides, shining with brilliant light.

This beautiful experiment is as interesting as it is strange and magical, and it illustrates both refraction and total reflection. The flask makes a lens, and the falling stream of water is lighted up by the cone of light that enters it at the hole in the flask. Both the water and the light pass out of the hole together, the light inside of the water. That this is so, may be proved by permitting the water to escape, when the light will be seen shining out of the hole horizontally into the room. Why, then, does it not shine out into the room while the water is escaping? When the stream of water is flowing out, it falls in a curve into the tub on the floor. The beam of light, passing out with the water, meets its curved surface at such an angle that it is totally reflected. This beam of reflection again meets the surface of the water, and is again totally reflected. In this manner

it is reflected from side to side, again and again, till it reaches the tub, and there we see it shining brightly. It is a prisoner in the water, and follows it down into the tub. When you put your hand in the falling water, you see that it is lighted brightly, and yet the stream by comparison is rather dark. If it were pure, distilled water, it would hardly be visible. As it is full of floating specks and motes, each of these reflects light, and these cause the water to appear full of light.

This fountain of fire is a charming experiment for a school, and its double lesson makes it as interesting as it is beautiful.

THE WATER-LANTERN.

Fig. 24 represents the water-lens used in the last experiment but two. The water-lens stands in the wooden box containing the mirror, and at the back of the box is a wooden slide holding a horizontal shelf at the top. This slide has a long slot cut in it, and, by means of a bolt and nut fastened at the back of the box, it can be made fast to the box in any desired position. This slide is 16 inches (40.6 centimetres) long, 5 inches (12.7 centimetres) wide, and inch (19 millimetres) thick; and the slot cut in it extends nearly the whole length.

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The shelf on the top is 7 inches (17.8 centimetres)

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