SoB Pi'of. Callan on a Contact Breaker 



per, pressure is not necessary. I have found that for working 

 this instrument; the magnetism of one pole of the core of an in- 

 duction coil is abundantly sufficient. When only one pole of 

 the core is presented to the armature, a piece of soft iron should 

 be fixed near the end of the armature opposite to that on which 

 the core acts. 



It will be useful to divide the induction coil and its core into 

 two or more parts, and to fix one end of each part of the core to 

 a frame, so as to be about ^'^th or ^^th of an inch from the 

 armature. The ends of the core presented to the armature 

 should be alternately north and south, and then the opposite ends 

 of the parts of the core will be also alternately north and south, 

 and may be connected with each other by a plate of iron, so that 

 all the parts w^ill act on the armature as one electro-magnet. The 

 various parts of the core should project at least an inch beyond 

 each extremity of the parts of the primary coil which surround 

 them. Both ends of each part of the core should be filed flat. 

 By connecting the ends of the parts of the core which are not 

 presented to the armature by a plate of iron, the magnetic 

 power of the core and its attraction for the armature, and con- 

 sequently the action of the contact breaker, is increased ; but the 

 sudden magnetization and demagnetization of the core is ren- 

 dered more difficult. I have used with the mercurial contact 

 breaker, a small coil divided into two equal parts, and have found 

 that the connexion of the ends with each other by an iron plate, 

 produced scarcely any change in the length of the sparks given 

 by the secondary coil. The sparks from the coil were longer 

 when the contact breaker was used, than any I was able to get 

 by making and breaking contact with the hand. The division 

 of the induction coil and its core into two or Jiiore parts will be 

 useful in long coils, because it diminishes the length of the wires 

 in the core. The parts into which the core is divided need not 

 be equal to each other in length. 



When the ends of the coil of an electro-magnet by which a 

 contact breaker is worked, are connected with a condenser, the 

 armature is, if the battery be small, instantly made to vibrate 

 more rapidly, and to strike against the poles of the magnet with 

 increased force, unless the contact be made and broken by mercury 

 and amalgamated copper, or some other amalgamated metal. 

 Such are the effects which I have found to be produced by the 

 condenser on the action of contact breakers in which the con- 

 tact was made and broken by means of mercury and platina, or 

 any unamalgamated metal, or by the pressure of two solid metals 

 against each other. But these effects were sensible only when 

 the battery employed was small. When a powerful battery was 

 used, the condenser gave no sensible increase of power to the 



