Constructive work; . one next the lamp thereis but one. Three wires, iron, copper, and brass are twisted togetherat one end and placed through the slit next the lamp. In the opposite end each wire passes through a slit. Bul-lets or small pebbles of equal weight arc attached to thesewires, (at equal distance from the light), by means of shoe- 255 makers wax. Heat is applied to the twisted end. The up-right part prevents the bullets or pebbles from getting anyheat by radiation. It therefore must be conduction. The wire from which the bullet first drops is the best con-ductor. This should be trie
Constructive work; . one next the lamp thereis but one. Three wires, iron, copper, and brass are twisted togetherat one end and placed through the slit next the lamp. In the opposite end each wire passes through a slit. Bul-lets or small pebbles of equal weight arc attached to thesewires, (at equal distance from the light), by means of shoe- 255 makers wax. Heat is applied to the twisted end. The up-right part prevents the bullets or pebbles from getting anyheat by radiation. It therefore must be conduction. The wire from which the bullet first drops is the best con-ductor. This should be tried several times before coming to adefinite conclusion. The pupils are now ready to understand what is meant bygood conductors and poor conductors. They »re now ready for the question of why we wearwool in the winter and cotton in the summer. Why so many animals in the frigid zones are coveredwith fur, those in the temperate zones with hair and many ofthose in the torrid zone with only thick skin. EXPANSION FIGURE XVIII. In connection with the study of heat the above exercisemakes a good problem in wood. The base is made of woodioxi^x3. The upright parts are 4 high. A dial isdrawn on the upright piece to the left. Just above the dialand near the top a piece of wood is thrust through 3. y%hole. A slit is cut into this circular piece of wood tO re-ceive a piece of tempered clock or watch spring which maybe had of .any watch-maker for only the asking. A piece of Y^ iron or brass wire is thrust into a hole inthe upright piece to the right and presses against a screwput in from the back. The other end is forced against the tempered clock springas shown in drawing. Heat is applied by placing the lamp in the center. Asthe v/ire expands the spring moves along the dial. 256 TEST TUBE HOLDER.
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