244- Prof. E. Wavtmann' sjburth Memoir on Induction. 



comes out of it*. These different systems are complicated, 

 and subject to several inconveniences. The rheotrope, which 

 I shall proceed to describe, and which is especially applicable 

 to electro-electric machines, combines with the advantage of 



* On the 18th of June, 1840, I communicated to the Society of Physics 

 and Natural History of Geneva an apparatus of this kind, the construction 

 of which presents no difficulty, and which is deposited in the Cabinet of 

 Physics in the Academy of Lausanne. The following is a description of it : — 

 " My commutator is composed of a pure copper stem a b (Plate II. fig. 1), 

 intersected in the middle by a piece of ivory c : the latter is hollowed into 

 the nut of a screw, in such a manner that the two halves of the stem screw 

 into it. Between these metallic extremities some sealing-wax is run, in 

 order to isolate them entirely. The cylinder thus formed is arranged ho- 

 rizontally, and each of its branches is furnished with symmetrical pieces at 

 equal distances. These pieces are two copper teeth ef, placed perpendi- 

 cularly and at a right angle on the axis ; then a copper circleg. Lastly, to 

 one of the extremities of the stem is fixed a pulley h, m the groove of 

 which there runs a ccrd i, which again passes over a lower pulley k, which 

 is much larger, vertical, and moveable by means of the handle m in one of 

 the supports of the apparatus. 



"The six projecting pieces of copper dip into a glass vessel w (fig. 2), 

 placed on two small horizontal barso; it presents six isolated compart- 

 ments full of mercury. The extreme circles remain immersed in tliis 

 liquid during the entire rotation of the stem, the arrangement of the teeth 

 causing one to be immersed whilst the neighbouring one is not. It is 

 easy to regulate the quantity of mercury in the troughs so that the immer- 

 sion of the one may correspond exactly to the exit of the other. 



" Supposing it be desired to emit into a rheometer the two induced cur- 

 rents, giving to them the same direction, it is sufficient to bring the extre- 

 mities of the wire in which the induction is produced in the extreme com- 

 partments reserved for copper circles. The ends of the wire of the mul- 

 tiplicator are tied to bars of copper connecting the troughs ef, ef, cor- 

 responding on the right and left of the isolator c to the needles fixed at 

 a right angle. So likewise on connecting the extremities of the rheometric 

 wire only with the troughs//, or with the troughs e e, it is evident that the 

 direct or inverted induced currents only may be collected. 



" I have combined with this arrangement one which M. Bonijol has 

 employed in some of his apparatus. It consists (fig. 3) of planting one of 

 the ends of the stem in a flattened wooden cylinder ?•, on which a spring s 

 presses, passing into a circular cylinder t of hard wood, and the free extre- 

 mity of which u is placed by the rotation of r in contact with an amalga- 

 mated metallic capsule x, or is removed from it. Then, by connecting the 

 spring on one side, and the capsule on the other, with the wire which the 

 direct current of the pile traverses, we obtain by the simple rotation of the 

 stem any number of inductions. 



"This apparatus enabled me to discover that the thermo- electric cur- 

 rents are capable of induction like the hydro-electric currents. I employ 

 a single bismuth-antimony pair, the solder of which is kept at 100° by steam. 

 The bismuth extremity is connected with the spring s, the antimony ex- 

 tremity with a wire covered with silk, which makes seventy turns on a 

 frame, and terminates at the capsule x. On the same frame is rolled an 

 isolated and finer copper wire which makes 1200 coils (110.), and both 

 ends of which terminate in the troughs p q. The induced circuit is closed 

 by a very delicate rheometer (5 a), which deviates five degrees and more, 



