204 APPENDIX. [No. XII. 



Such a circle of atoms is called a voltaic circuit, and the apparatus in 

 which the action is performed, a voltaic battery. 



The decomposable substance, which forms the basis of the battery, is 

 called an electrolyte ; and the substance which decomposes it, by exerting a 

 strong attraction on one of its elements, is called the positive element of the 

 battery. The simplest idea of a voltaic circuit is presented by a particle of 

 water and a particle of zinc; in which the zinc presenting an attraction 

 for oxygen in the reverse direction to that of the hydrogen, the former 

 unites with the metal, the latter is given off. But 



" Had we no means of increasing the length of the interval between 

 the abstraction of one element of the electrolyte, by the new attraction 

 exerted between it and the positive pole and the evolution of the second 

 element, voltaic batteries would be but of little advantage. But we have 

 the power of increasing this interval indefinitely ; sometimes miles inter- 

 vene between those two points. 



" The mode in which we increase this interval depends upon the power 

 of the new attraction exerted between the zinc and oxygen of the water, to 

 propagate the tendency to the destruction of the old attractions of 

 hydrogen and oxygen through a series of particles of fluid. A second 

 point is then placed, at which the hydrogen, or second element, may be 

 evolved. This second point is the negative element." P. 75. 



We thus see that the positive pole or element is the source of all the 

 phenomena manifested in the voltaic circuit. The degree of their energy 

 is the degree of chemical attraction exerted between that positive pole and 

 one element of the electrolyte. Whatever can be an obstacle to chemical 

 affinity can also be an obstacle to voltaic action. 



These obstacles may be briefly stated thus : 



First, there is the previous attraction existing between the two 

 elements of the electrolyte to be overcome. The best way of countervail- 

 ing this seems to be (supposing water the electrolyte as it generally is), to 

 place at the negative pole some substance, holding oxygen in a loose state 

 of combination, with which the hydrogen may combine at the moment 

 of its liberation; so that the hydrogen, finding a new affinity exerted 

 towards it, may be more ready to relinquish its oxygen to the zinc. This 

 is the theory of Professor Daniell's battery, in which sulphate of copper is 

 placed at the negative pole, and is reduced by the nascent hydrogen, and 

 of Mr. Grove's, in which the same purpose is effected by nitric acid. 



A second and third obstacle are offered by the force with which the 

 particles of fluid are kept in their situation, and by the force with which 

 the particles of metal cohere. 



A fourth is frequently presented by the formation of a new compound 

 at the positive pole (sulphate of zinc), which prevents the zinc from coming 

 into contact with the electrolyte. 



Hence it is evident that the measure of the intensity of the voltaic 

 circuit is equal to the excess of the attraction of the positive pole for one 

 element of the electrolyte, over the force exerted by these impediments. 



Mr. Smee next speaks of the compound voltaic battery disposes very 

 summarily of that theoiy which attributes the production of electrical 

 effects to the contact of metals, and mentions the mode in which the 

 voltaic force effects the decomposition of binary compounds in a state of 

 solution ; and then treats at some length of tension, that is to say, " a desire 



