Prof. E. Wartmann* s^^ntrth Memoir on Induction, 243 



2. To render it discontinuous, and in alternately contrary 

 directions. 



This current being employed to react on a wire B, near the 

 conductor A, it may be required — 



3. To isolate the direct currents, induced from the closing 

 of the circuit A ; 



4. To isolate the inverted currents, induced on breaking 

 this circuit; 



5. To emit these currents successively, giving them the 

 same direction ; 



6. To emit them alternately in contrary directions, just as 

 they are produced directly. 



It is known that there is a reaction of the induced currents 

 on the principal current. We may therefore desire — 



7. To collect the totality of their reaction; 



8. To avail ourselves only of the reaction of the direct in- 

 duced currents; 



9. To avail ourselves only of that of the inverted induced 

 currents ; 



10. To collect only the induction of the inductor on itself. 

 120. Physicists have studied the majority of these cases; 



but the mechanical instruments which they have imagined and 

 described under the names of disj'unctor^, tachytrope\, rheo- 

 tropeX, gyrotrope^^ or co7nmutator\\, are scarcely applicable 

 except to one or other of the first two categories. The most 

 complete of these instruments, reinvented in Paris seven years 

 after having been described and employed in Germany, is 

 composed of four isolated wheels on the same axis, the outline 

 of which presents successively metallic and ivory arcs, against 

 which press conducting springs. The axis is set in motion by 

 means of a handle or tooth-wheel. Sometimes the interval of 

 the teeth is left void, and the spring in escaping determines 

 the opening of the circuit. Other commutators are formed 

 with needles arranged on isolated axes, in such a manner that 

 one is immersed in mercury at the instant when the other 



* Dove, Magneto-elektrischcr Apparat zum Hervorbringen inducirter 

 Strome gleicher hitensitdt in von einander vollkommen getrennten Dr'dhten 

 Pogg. Ann., vol. xliii. p. 51 1 . ] 838. 



"^ Dove, Ueber den Gegenstrom zu Avfang tend Ende eines prim'dren, 

 Pogg. Ann.y vol. Ivi. p. 251. 



X Masson et Breguet, Memoirc sur ^induction. Ann. de C/i. et de Phys.t 

 vol. iv. p. 134. 1842. 



§ Pogg. Ann., vol. xxxii. p. 539 ; and vol. xxxiv. p. 18S and 500. 

 1834-35. 



II Jacobi, Sur P application de V Eleclro-magnetisme au monvement des via- 

 chines, § VII. Potsdam, 1835. Taylor's Scientific Memoirs, vol. i. p. 503, 

 4rcMvc'8 de PElectr., vol iii. p. 244. 



R2 



