Prof. E. Wartmann's/owr^i^ Memoir on Induction. 245 



being more simple, and consequently less subject to derange- 

 ment, that of not requiring the employment of mercury, and 

 of serving to solve all the cases above stated. 



121. H (Plate II. fig. 4) is a reel on which two insulated 

 wires are wound ; one the inductor A, by which the current 

 of the battery j9 n is made to pass; the other the induced B, 

 intended to become the seat of the currents of induction. 

 Three brass wheels r, 5, t, of the same diameter, are isolated 

 from one another on a common axis; their circumference pre- 

 sents an equal number of parts alternately of metal and wood. 

 Two metallic springs a, b are fixed against the wheel r, in 

 such a manner that the first leans against a conducting arc, 

 and the other against an insulating arc. The wheels s and t 

 are each pressed by two springs c d, ef^ similarly arranged. 

 The central metallic parts of the three wheels are in constant 

 communication with the springs ^, ^, i. 



122. If it be desired to collect the voltaic current always in 

 the same direction after having rendered it discontinuous, it is 

 sufficient to connect the spring / with the pole p by a wire «, 

 and the other pole n with the spring^ by means of any con- 

 ducting wire different from the wires A and B wound upon 

 the reel. If it is wanted to obtain, as with the inversor, the 

 discontinuous current in directions alternately contrary, we 

 must join the springs c and e as well as the springs d and/j 

 and then connect the extremity of the conjunctive wire of the 

 battery with the spring h. 



123. When it is desired to employ currents of induction, 

 the contact of the extremity / of the inducting wire with the 

 pole w is established permanently, and that of the extremity m 

 with the spring/*. Now, to isolate the direct currents induced 

 at the closing of the circuit A, we have only to connect the 

 ends x and y of the wire B respectively with the springs h and 

 g. — To isolate the inverted currents, we unite .r with h and y 

 with d. — To cause the direct and the inverted currents to pass 

 one after another in the same direction through the rheometer 

 G, for example, we connect the springs a and c with the end 

 s of the wire of the instrument, the springs b and d with the 

 end t, the extremity x with the spring h, and the extremity y 

 with the spring g. — To collect the induced currents alter- 

 nately in contrary directions, just as they are produced directly, 



when it is traversed by direct and inverted currents in the same direction." 

 (See the Transactions of the Helvetic Society of Natural Sciences for 1840, 

 pp. 173, 195.) 



Prof. Dove has demonstrated thermo-electric induction by a different 

 process. His researches were made at the same time as mine, and in an 

 independent manner. (See Pogg. Ann., vol. xlix, p. 97* 1840.) 



