108 
MR. GROVE ON THE GAS VOLTAIC BATTERY. 
cathode is that they are correlations ; although they take place at a distance, the one 
has no more been proved to take place without the other, or before the other, than 
height has been proved to exist without depth. I therefore allude to this hypothesis, 
not as literally adhering to it, but because it is generally received, and may tend to 
associate the action of the gas battery with the ordinary phenomena of electrolysis. 
A number of hypotheses has been and may be proposed to account for these and 
other mysterious phenomenal relations ; they all agree in being assimilations of what 
is unfamiliar to what is familiar. They are undoubtedly useful as didactic illustra- 
tions, and it is as such that they have hitherto contributed to advance science. It is, 
however, a curious circumstance, and worthy of some consideration, that the voltaic 
hypothesis of Grotthus, the emissive and undulatory hypotheses of light and heat, 
and, as far as I am aware, all physical hypotheses hitherto propounded, represent 
natural agencies as effects of motion and matter. These two seem the most distinct, 
if not the only conceptions of the mind, with regard to natural phenomena, and when 
we try to comprehend or explain affections of matter which are not obviously modes 
of 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 con- 
ception ? 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 inquiry 
would 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 immedi- 
ately 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 effi- 
cient 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 sequence of time in the 
phenomena, the contact or completion of the circuit and the electrolytical 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 con- 
tact an idea of force which does or may produce a voltaic current independently of 
