THK THEORY OF SENSATIOX. 181 



whicb our mind perceives, but only their images or representations 

 impressed upon the sensorium." I add, only, the statement of David 

 Hume. " Xoihiug can operate in a time, or place, which is ever so 

 little removed from those of its existence." Whatever new difficulties, 

 therefore, the " sensible species" of Aristotle involved, they, at least, 

 seemed to do away with that which was deemed insunnountable, 

 perception, and, therefore, agency at a distance. 



On this reasoning let me observe first, that those who have 

 employed in their argument the assumed axiom referred to, seem 

 to have had reference primarily to efficient or metaphysical, not to 

 physical causes. They regarded it as an utter impossibility that 

 what might be properly regarded as an active cause or efficient 

 agent, could, by the exercise of its own energies, produce any effisct 

 whatever upon objects distant from the place in which it might be 

 said to be essentially present. On this dogma, I can merely say, 

 that it seems to me to be destitute of proof, although, by others it has 

 been regarded as self evident. But, then, granting the position, I object 

 to the arguing from efficient causes to physical, and to the employ- 

 ing as an axiom in subjects of the latter kind what is true, if true, 

 only of the foraier. It may be the fact that there is no efficient 

 causation at a distance, but of efficient causation we know nothing, 

 as I shall remark presently ; in science we have to do only with 

 physical causes, that is, with bare antecedents ; and that there can 

 be no causation of this kind at a distance is contradicted by daily 

 experience, for example, in all the phenomena of gravitation. The 

 earth attracts bodies suspended in the atmosphere ; the moon raises 

 up the waters of ocean; and the sun, without moving from his 

 throne, binds in faithful allegiance, and continually counteracts the 

 tangential impulses of worlds, whose distance from the august seat 

 of empire, defies not the powers of numbers to calculate, but 

 certainly the powers of thought to realise. 



But we need not rely merely on the refutation of the false 

 maxims, and erroneous application of them, by which the theory 

 referred to was upheld. We can account for the phenomena it was 

 framed to explain in some better way, even the sure discoveries of 

 science. We have found, by the way of induction, what are the 

 true links between the remote object and the organ of sense. In 

 cases of vision it is ascertained, not to be the object itself, but rays of 

 light from it which affect the optic nerve. Thus, were a star anni- 

 hilated, we should, for a length of time proportioned to its distance, 

 continue to perceive it, because the light which it had transmitted 

 before its extinction would not all have reached us ; and were a star 

 newly created, it might be years before it became visible, as it might 

 require that period lor the light which affects the organ of sight to 

 traverse the vast interval. So in cases of sound, it is vibrations of 

 the air which affect the nerve ; in taste, it is particles of the sapid 

 body ; in smell, it is particles of the odorous substance ; and in 

 touch, it is of course the presence of the object itself. 



The substance of our reply, then, to the ancient theory, for 

 accounting for the effect of the distant object on the organ of sense 



