254 Electro-Magnetic Apparatus and Experiments. 



solid bar for reaction upon the coil loires. Mr. BachofFner proba- 

 bly used this compound arrangement before myself, as I made 

 the discovery February 14th, 1838. Mr. BachofTner remarks, 

 "that it is necessary to insulate the wires of the bundle, and that 

 it is difficult to understand their action, as the magnetic power is 

 not so great as that of a solid bar." In every experiment hith- 

 erto tried, I have invariably found the magnetic power to be 

 greater than that of a solid bar of the same weight. I have 

 never found it necessary to insulate the wires to insure their ope- 

 ration, although I would not say that a very careful insulation 

 might not improve their operation. For I apprehend that in the 

 development and return of magnetic forces, electrical currents are 

 excited in the body of the magnet at right angles to its axis, as 

 well as in the wires surrounding the magnet. In this case the 

 exterior portion of the magnet would act as a closed circuit upon 

 the interior. 



By a closed circuit is meant a flowing secondary current, 

 which has the effect to re-magnetize the bar after the primitive 

 battery current has ceased to act. That the operation of these 

 secondary closed circuits has never yet been considered in the 

 construction of machines, will appear from the following facts 

 and practical observations. 



First. — Enclosing a compound* electro-magnet in a tube of 

 metal, almost entirely prevents the formation of secondary cur- 

 rents in the exterior wires, although by this arrangement the 

 magnetic power is not perceptibly affected, with the exception, 

 that its development requires more time.-f The short and com- 

 plete right angle currents in the metallic casing have a greater 

 magnetizing power than the secondary of an extended and ob- 

 lique coil of wire. Hence, after the battery current ceases, the 

 chief portion of the secondary will flow in this short circuit, and 

 the magnetism of the bar be prolonged to a perceptible degree, 

 and if it were possible to break this closed circuit immediately 

 after the battery circuit, a secondary and tertiary current would 

 be observed from the coil of wire. This tertiary circuit I have 

 perceived in another way. 



^ Or a common single magnet. 



t The increase of time necessary to effect the full development of magnetism, 

 is due to the formation of the initial secondary flowing against the battery curreut. 



