294 Researches in the Theory and Calculus of Operations. 



forming an instantaneous current which again disturbs the 

 galvanometer, and equilibrium then directly follows in the 

 system. The operation of alternately connecting and dis- 

 missing the wires of AA X with the battery may be repeat- 

 ed ad libitum, may be repeated indefinitely, always with the 

 same result (Ruhmkobff). 



The coiled wires are insulated to prevent cross transmis- 

 sion of force. The induced coil of B is greatly increased in 

 length and reduced in diameter beyond the length and 

 diameter of the coil of A, thereby enhancing the quality 

 of the former coil at the expense of the quantity of the 

 latter, in order to encourage a quick reaction when the 

 battery connection is broken ; which connection should be 

 quickly resumed, ere the slower return discharge through 

 b" 'A a" can take place; an evil, however, which may be 

 partially remedied by the use of a condensator. 



We have here an analogue, albeit under an exalted degree 

 of energy, of the simplest form of electrical excitement 

 (fig. 28). When the excitor E is pressed against the excitee 

 E', a current of force travels across the latter from O, and 

 appears in tension on the surface at a : whenE is withdrawn, 

 reaction returns the interfering force to 0, and equilibrium 

 is restored. Precisely similar is the communication between 

 the extremities b' n and a'" of the wire wound cylinder 

 BB 1? the wire wound cylinder AA X being the excitor dis- 

 charging force upon the extremity b ,n of the former cylin- 

 der. The continued successive applications of the frictional 

 pressures and withdrawals in the operation of the electrical 

 machine are here effected by means of the interruptor and 

 commutator (Foucault). 



In addition to the above attempted explanation of the 

 reverse current of BB 1? it remains to be observed that the 

 whole course of the current of the wire of AA X may act 

 inductively and through the dielectric medium between the 

 cylinders, upon the stationary forces in the wire of BB^ 



