GAS BATTERY. 279 



motion, we hypothetically or theoretically reduce -them to it : 

 the senses perceive the different effects of sound, light, heat, 

 electricity, &c., but the mind appears capable of distinctly 

 conceiving them only as modes of motion. Does not this supply 

 an argument that all physical agencies are reducible to these 

 elements of mental conception ? Or are we to look for new 

 powers of mind, in other words, will greater familiarity with 

 phenomena, at present recondite, enable the mind more clearly 

 to comprehend them, and avoid the necessity of referring 

 them theoretically to more familiar and apparently more 

 simple phenomena ? To pursue this curious enquiry \vould 

 involve me in a discussion foreign to the object of this paper 

 and to the general character of contributions to the Royal 

 Society, but the question arises so immediately out of the 

 subject, and is so necessary to explain my own view, that I 

 trust this brief statement of it will be considered sufficiently 

 pertinent. It touches upon that interesting, scarce definable 

 boundary, where physical merges into metaphysical science. 



There are one or two other theoretical points as to which 

 the gas battery offers ground of interesting speculation ; the 

 contact theory is one. If my notion of that theory be correct, 

 I am at a loss to know how the action of this battery will be 

 found consistent with it. If, indeed, the contact theory assume 

 contact as the efficient cause of voltaic action, but admit that 

 this can only be circulated by chemical action, I see little 

 difference, save in the mere hypothetical expression, between 

 the contact and chemical theories ; any conclusion which 

 would flow from the one would likewise be deducible from the 

 other ; there is no observed sequence of time in the pheno- 

 mena : the contact or completion of the circuit and the electro- 

 lytical action are synchronous. If this be the view of contact 

 theorists, the rival theories are mere disputes about 'terms. If, 

 however, the contact theory connects with the term contact 

 an idea of force which does or may produce a voltaic current 

 independently of chemical action, a force without consump- 

 tion, I cannot but regard it as inconsistent with the whole tenor 

 of voltaic facts and with general experience. 



Another point of theory suggested by the gas battery is 

 the relation of latent heat in the different cells of the battery 



