Popular Science Munllihj 



799 



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 



END5 Of WIRES 

 TOUCHED TOGETHER 



BATTERY 

 CEIXS 



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. 



