836 EECENT PROGRESS IN PHYSICS. 



§ 57. Magnetizing hy the main current. — To avoid false conclusions 

 in regard to magnetizing by the secondary current, magnetizing by 

 the main current should first be properly investigated. 



Such an investigation was first made by Savary. Riess repeated 

 Savary's experiments and obtained similar results. The following 

 are Riess' results. — (Pog. Ann. XLVII, 55.) 



In the conducting circuit of the battery, consisting of 25 jars with 

 l.j square foot coating each, a spiral of platinum wire was placed ; 26 ' 

 inches of this spiral were wound in 42 coils on a glass tube 3 inches 

 long. The ends of the wire not wound up were, together, 34 inches: 

 long. 



In each experiment a new non-magnetic English sewing needle,L 

 13-9 lines long and 0.19 lines thick in the middle, was laid in the 

 spiral. After the discharge stroke had passed through the spiral thei 

 needle was magnetized. To test the strength of the magnetism iti 

 was brought to a certain distance from a compass needle two inches, 

 long, (in what manner this was done cannot be easily understood from 

 Eiess' description,) and the deflection produced in the latter observed.! 



By increasing the charge of the battery, not only the strength but; 

 the polarity of the magnetism of the needle changed; as the following 

 table shows: 



Quantity, 5 10 15 20 25 27 29 30 32 35 



Deflection, 9° 14.5 15 10.3 6.5 — 2.5—7.5 — 8.5 2.3 11.5 



It is seen that a stronger charge of the battery was not necessarily 

 followed by a stronger magnetism ; also, that the magnetism thusi 

 caused was not always such as might have been expected, according tof 

 Ampere's rule, (namely, that if we suppose the figure of a man to be 

 introduced into the circuit, the positive current entering at the feet 

 and passing out at the head, the figure, when it faces the needle, will 

 have the north pole on its left hand,) for an abnormal magnetizing of 

 the needle took place in all the deflections marked with the — sign. 



In this series the strength of the magnetism of the needle at first 

 increased with the magnitude of the charge, then decreased until the 

 direction of the magnetism was reversed, and it was only after still 

 more powerful charges that the normal magnetism appeared again. 



These experiments are a proof that the direction of the discharge 

 current cannot be deduced from the polarity of the needle. 



With weaker charges the needle was normally magnetized ; abnormal 

 magnetism appeared with increased charges in fine needles only ; 

 coarse needles are always magnetized normally, although constantly! 

 increased charges produce in them an alternate decrease and increase 

 of strength of the magnetism. 



§58. Magnetizing hy the secondary cury-ent. — This peculiarity in the 

 magnetism of steel needles occurs in like manner in the secondary 

 current. Magnetism produced by a secondary current will change in 

 strength and direction: 



1. By increasing the charge. 



2. By increasing the surface of the battery, the charge remaining 

 the same. The greater the surface, the stronger Riess found the mag- 

 netism of the needle ; the same quantity of electricity being distributed 



