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Page:Popular Science Monthly Volume 89.djvu/813

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Popular Science Munllihj


��Simple Method of Remagnetizing Magnets

REMAGNirnZINC. magnets is a very simple oiHT.ilidii for which about lOO ft. (jf No. iiS copper wire, a i2-volt storage-battery current and a small pocket needlecompass arc required. I-'urthermore, the magnet may be tested for strength after it has been removed from the magneto and again tested after it has undergone the remagnetizing process by means of another simple e(|uipment consisting of a block of wood, a bar of iron, a Hat iron-plate, a spring- balance scale and a piece of non-con- ducting cord. Both of these equipments as used are shown in the two accompan^•- ing drawings.

The method of jjrocedure after remov- ing the magnet from the magneto is first to test its strength. This is accomplished as shown in Fig. 2. The block of wood is held in a vertical position in the jaws of a vise or other handy object and a rod with a hook at its end is slipped into a staple and plate screwed to the top of the block of wood. A spring-balance scale with a ring at the top is suspended from the rod, the mag- net being iiung from the scale by a strong cord but with the two ends touching a clean flat iron-plate laid on the bench beside the vise. On account of the magnetism remaining in it when re- moved, the magnet will tend to adhere to the flat iron-plate; it can be pulled away by pushing up on the rod, at the same time registering the pull on the spring-scale. After this has been done several times and the pull registered each time, calculate the a\erage pull to release the magnet and the area in contact with the flat iron-plate. If the pull required is less than 30 lb. per square inch, the magnet is weak and should be remagnetized as shown in Fig. i.

The 100 ft. of wire should be formed into two equal coils into which the legs of the magnet can be inserte<l. The polarity of the coils should be tested by means of the pocket needle compass and the current from one of the dry cells, the needle being attracted by one coil and repelled by the other. Then test the magnet itself by means of the compass and place the positive magnet leg in the positive coil and the

��negative leg in the negative coils. This is of great importance; for if the positive leg is inserted in the negative coil, the IJolarity of the magnet will be reversed and it will become useless. Next wire up the end of the coils with the three cells as shown, with a break in the circuit. The magnet is remagnetized by alternately bringing together the ends of the wire at the circuit break and then pulling them apart. This operation should be continued for about five minutes, after which the magnet should be tested as described above. If the magnet does not show enough strength the first time, the remagnetizing process should be repeated until it does. This



���Fig. 2.

��Fig. 1. Method of remagnetizing magnets Fig. 2. Calculating the strength of the magnet

accomplished, an iron keeper should be placed across the magnet legs so that its strength will not be dissipated through the tendency of the magnetism to jump the air gap between the poles if left free. — Joseph Brinker.

��The Telephone Receiver for Wireless Apparatus

THE telephone receiver used in wire- less telegraphy is a very sensitive instrument, and gives signals from ex- ceedingly small amounts of electrical power passed through its magnet w'ind- ings. Nevertheless, measurements have shown that only about one one-him- dredth of the power applied electrically is actually converted into sound-w.ives.

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