1. How is heat transferred from one body to another? 2. Could chicks or pigs receive warmth from a heat lamp without the air in the pens becoming warm? Explain. 3. How does a broiler unit in a range cook meat? 4. How does an oven bake food? 5. Tell why iron picture wire was used instead of copper wire for your heating demonstration. LESSON NO. B-13 Credit Points 2 MYSTERIOUS MAGNETISM In ancient times, people found certain rocks that clung together in bunches. These rocks were very mysterious. People didn't understand them and many superstitions grew up about lodestones, as these rocks were called. Lodestone (sometimes spelled loadstone) means leading stone. People even told Columbus not to sail out of sight of land because a giant lodestone was just over the horizon waiting to pull all the nails out of his ships. The Chinese were the first to use magnets. They found that if you hung a lodestone by a string, one end of the stone would always point in the direction of the North Star. They had the first magnetic compasses. An artificial magnet can be made by stroking or gently rubbing a piece of steel with a lodestone. This piece of steel then can be used to magnetize another piece of steel. This can be continued on and on. Lodestones are not always available but you can get the same results with an electric current. So, magnetism and electricity are very closely related. What to Do Learn about magnetism by doing the experiments that follow. Seeing is believing! Materials You Will Need 2 dry cell batteries (#905) A few feet of No. 18 bell wire 3 steel knitting needles or similar hard steel 2 ft. of light thread Sheet of light cardboard or stiff paper Permanent magnet (bar or horseshoe) Compass 1 or more large nails or spikes Red and black china-marking pencils or crayons Iron filings Wire cutters Carpet tacks (Iron filings usually can be found under the grinding wheel in a shop. If you can't find any, rub some steel wool pads together to produce bits of metal that will do.) "See" a Magnetic Field Cover the permanent magnet with the cardboard or paper. Sprinkle iron filings on the paper. Tap the paper and note the pattern formed. Strings or lines of filings pass from one pole of the magnet to the other. The area covered by the filings is the center of the magnetic field. To remember this, you might compare the magnetic lines of force that arrange the iron filings to the contour strips in a farmer's field. This magnetic field is one of the important things in our everyday life with electricity. If it were not for the magnetic field, we would not have electric motors. Telephones, radios, television, and many other things we use every day also depend on this magnetic field. [Illustration: Figure 1] Make an Electro-Magnet