GALVANISM. 



Couronne de tosses. If the circuit be 

 interrupted at any one point, by remov- 

 ing one or more of the vessels, the in- 

 strument is rendered similar in its opera- 

 tion to the pile, and the metallic plates 

 at each end of the series which are not 

 immersed in fluid, may be connected to- 

 gether by means of wires in order to 

 complete the circuit. Such an arrange- 

 ment is shown in fig. 8, where the zinc 

 Fig. 8. 



and copper plates are marked respec- 

 tively with the letters Z and C : and the 

 course of the electric fluid denoted by 

 the arrows. 



(14.) It is also to be observed, that in 

 every compound galvanic circle, such 

 as is exemplified in this apparatus, the 

 direction of the electric current is pre- 

 cisely the same as in a simple galvanic 

 circle composed of the same elements. 

 In the present case, where zinc and cop- 

 per are the metals employed, and the 

 fluid acts upon the former so as to oxi- 

 date it, a stream of positive electricity is 

 continually circulating from the zinc to 

 the copper plate contained in the same 

 vessel, through the oxidating fluid which 

 separates them ; and is transferred from 

 the copper to the zinc plate contained in 

 the next vessel, along the slip of metal 

 which connects them. Following its 

 course in this manner to the end of the 

 series, we find the electric current pass- 

 ing on from the last copper plate, con- 

 tained in the last vessel, to the zinc 

 plate connected with it, and thence con- 

 veyed along the wires of communica- 

 tion, round to the copper plate at the 

 other end of the series. The direction of 

 this current is shown in the figure by 

 the arrows above and below. It is evi- 

 dent, therefore, that that end of the bat- 

 tery which is terminated by a zinc plate 

 is that from which electricity is given 

 out to the wire, and is, consequently, the 

 positive end, or pole, as it is called, of 

 the battery. For the same reason, the 

 opposite end, or that terminated by the 

 copper plate, and which receives the 



electricity from the wire, is the negative 

 pole. The same observations apply to 

 the galvanic pile ; the zinc end being the 

 positive, and the copper (or silver) end 

 the negative pole. 



(15.) It will be perceived that the de- 

 nominations of the zinc and copper ends 

 of the pile or compound battery, as being 

 positive and negative, are exactly the 

 reverse of what obtains in the single 

 galvanic circle, where, as we have seen, 

 it is the copper plate which is positive, 

 and the zinc negative, with relation to 

 the communicating wires. But as the 

 direction of the electrical currents is the 

 same in the compound as in the simple 

 circle, this contrariety in the qualities of 

 the poles appears, at first sight, para- 

 doxical. But the difficulty vanishes 

 when we advert to the circumstance, 

 that in the simple galvanic circle the 

 conducting wire communicates directly 

 with that plate which is in contact with 

 the fluid part of the apparatus ; while in 

 the compound circle it proceeds, not 

 from the plate immersed in the fluid, but 

 from that which is associated with it, 

 and, therefore, of a different kind. The 

 compound circle reduced to its condition 

 of greatest simplicity would be repre- 

 sented by the following series, consisting 

 of five parts, namely, 



copper zinc fluid copper zinc. 

 In this arrangement the copper end is 

 negative, and the zinc end positive. By 

 merely removing the two terminal plates,* 

 which, in fact, are no ways concerned 

 in the effect, we bring it to the state of 

 the single circle, consisting simply of 



zinc fluid copper : 

 here we find the zinc end negative, and 

 the copper end positive. It is highly ne- 

 cessary to possess clear ideas of this dif- 

 ference, since much ambiguity has arisen 

 from inattention to it in describing ex- 

 periments, and reasoning upon their 

 results, more especially in the study of 

 electro-magnetism, hereafter to be con- 

 sidered. 



(16.) A much more compendious 

 form may be given to a battery con- 

 structed on the., principle of the Cou- 

 ronne de tasses, by employing a trough 

 divided into numerous compartments by 

 partitions, the whole being made of non- 

 conducting materials. This will admit 

 of the plates being brought nearer to each 

 other, and of a much greater number 



* Volta, in conformity with tlie theory he had 

 adopted, considered these terminal plates as adding 

 to the galvanic power. Bat we shall afterwards point 

 out the incorrectness of that theory. 



