188 LOCALIZED ELECTRIZATION. 



a wooden disk that turns upon its axis ; and to this disk are attached trans- 

 verse brass springs, indicated by the dotted lines a', V, c', d', e',f', //', A'; the 

 fii'st transverse spring, a' , forms a communication between the knob that 

 receives the positive pole 1, and the knob 2', which is connected with the 

 negative pole ; and so on, throughout the remaining springs. The disk is 

 moved by the knob E ; and when this is pushed to E all the sections are 

 united. In other words, P, the terminal positive pole of the first section, 

 commrmicates with the initial negative pole of the second section, by passing 

 through r, «', 2', and «"; and so with the remaining sections. The sections 

 should only be thus combined during the application of the current. 



8. If, during the repose of the pile, the knob E is returned to its original 

 place, the sections are again separated, the transverse metallic springs no 

 longer connecting the terminal positive pole of each section with the initial 

 negative pole of the next. 



I. The apparatus serves, moreover, to distribute the currents of the battery 

 X, either in fractions or as a whole, and thus graduates the electro-motor 

 power. The distributors of the currents are the handles B, C, wliich conduct 

 them in the following manner to the knobs N, P, which receive the con- 

 ducting Avires of the rheophores. The handle C carries a copper spring, shown 

 in fig. 49, which can be placed in contact with any one of the pieces of copper 

 of the surface A A, and wliich communicates by its axis D, also of copper, 

 and with the knob P by the line D'. The handle B carries a double metallic 

 spring, N', G' ', one blade of which communicates with the metallic circle, G, 

 and the other with any one of the pieces of copper which receive conductors 

 from each section of the battery. 



5. It often happens, in actual use of the battery, either for the therapeutic 

 application of continuous currents, or to work induction instruments, that 

 only a portion of the whole is required. If the same portion were always 

 employed, the battery would be exhausted in an unequal manner. By a 

 simple change of the handles, we may easily and quickly bring into alternate 

 tise the first, middle, or last third of the whole. If, for example, it were 

 wished to use only the last twelve elements, the handle B should be placed 

 over the knob 7 j>, and the handle C over the knob 8 i>. 



The apparatus lastly becomes, when required, a commutator or reverser of 

 the poles. For this purpose it is only necessary to change the sides of the 

 handles, the rheophores resting undisturbed over the parts subjected to 

 the current. In all the movements of the handles, the contacts are so dis- 

 posed as to avoid intermissions of the current. 



Graduation of galvanic currents. — The power to increase or 

 diminish at pleasure, and rapidly, without any interruption of the 

 circuit, by tens of elements at a time, the current from a large 

 battery, may be considered as a graduation of its electro-motor 

 force. This is obtained, as we have just seen, by the instrument 

 above described. 



But it is often also required to diminish gradually, at pleasure, 

 the calorific and electrolytic action of the battery, the number 

 of elements remaining the same. For this purpose, I cause the 

 current to pass through a layer of liquid of greater or less thick- 

 ness contained in a glass tube that I have called a moderator, and 

 that will be fully described hereafter. The liquid, which should 

 be distilled water when the tube is used for the graduation of 

 an inductive, and more especially of an induced current, should be 

 replaced by water saturated with sea- salt when it is used to 

 graduate voltaic currents, the tension of which is feeble, as com- 



