TRANSACTIONS OF THE SECTIONS. 169 



the Tibration of the air comes into conflict with the living thrill of the uen'e,. and 

 how the result of this conflict reaches the mind, wc are at present unable to com- 

 prehend. It is one of those hidden secrets of nature which science has not yet been 

 able to unfold. Turning from the sense of hearing to that of sight, a precisely simi- 

 lar analysis holds good. Here the vibrating medium is not the atmosphere, but a 

 universally diff'used ether which is set in motion by what are colled luminous bodies. 

 Just as atmospheric oscillations form the external cause, and sound the internal 

 result, in the case of hearing, so in sight the oscillations of the light-bearing ether 

 form the outward condition, and colour, in all its various shades, the inward result. 

 Here, accordingly, as before, it is simply motion in natui'e giving rise to motion in 

 the nerve-world with which we have immediately to do in vision ; while, to keep 

 up the analog}-, it is the difierence in the rapidity of the oscillations that creates all 

 the infinite variations of hue. The red rays, it is calculated, require 458 billions 

 of oscillations in a second, the violet rays 727 billions, and all the other colovurs and 

 shades of the spectrum some intermediate number. That the phenomena of sound 

 and sight spring physiologically out of particular states of the corresponding nerves 

 is clear from the fact that pressure on the eye, or any artificial irritation, produces 

 the perception of light as strongly as the normal impiilses derived from the vibrating 

 ether, and that any artificial excitement of the auditory nerve will produce noise in 

 the head. Ghost-seeing often arises in the same way — that is, when the conditions 

 of sight are brought about by the nerves being aflijcted through some other than 

 the ordinary and legitimate stimidi. Whatever, in a word, can aftect the regular 

 vital movements of the nerves, and put them into a condition at all similar to that 

 produced by the proper external stimuli of sensation, ^vill, of necessity, bring about 

 similar phenomena of consciousness. We come next to the sense of feeling. This 

 sense comprehends two appai-enlly distinct series of sensations, namely, those of 

 touch, properly so called, and those of heat. With regard to the latter, it has been 

 pretty well established that the phenomena of heat originate in the oscillations of 

 a subtle fluid similar to that of light. The sensation of heat maj', therefore, be 

 brought under tlie law of motion just as much as that of light or hearing, and may 

 be regarded in every respect as analogous. The phenomena of touch, we know, are 

 produced by impact in various ways ; and it is just in accordance with the nature 

 of that impact, whether harder or softer — more rapid or more slow — that the result- 

 ing sensations are deteiiniued. A blow is a sudden afl'ection produced by the rapid 

 motion of some object against a considerable surface of the bodj'. Pressure is a 

 more continuous affection of the same kind. A prick is the motion of some object 

 against one minute point of the skin. If the act of pricldng be repeated rapidly, it 

 produces a feeling of burning, and, if it be very soft, at the same time of itching. 

 An extremely light and gentle motion over the body produces tickling. In every 

 instance the peculiar kind of sensation is determined by the natm-e of the motion 

 and the consequent impact. The only two senses left, accordingly, are those of taste 

 and smell. In both these cases the process by which the nerves are affected is of 

 a chemical nature. The substances received upon the surface of the tongue or the 

 internal membrane of tlie nostril are subjected to the action of saliva or mucus, and, 

 being thus dissolved, produce a chemical action on the nerves, which gives rise to 

 the phenomena of taste and smell. All chemical action, however, arises, as far as 

 it can yet be ascertained, from certain relative movements in the ultimate atoms of 

 bodies, and it is these movements which, in the case of taste and smell, really give 

 rise to the peculiar sensations so designated. One striking proof of this is, that a 

 similar atomic action can be produced by magnetism, and that various tastes, par- 

 ticularly that of phosphorus, can be produced by the introduction of magnetic plates 

 into the mouth ; thus most obviously proving that the phenomena of taste are reaUy 

 produced, like those of heat, by the motion of certain minute particles, whether of 

 some magnetic fluid or of anytliing else, when subjected to chemical action. By 

 these atomic movements the nerves are affected, just as they are affected by the 

 infinitesimal oscillations of light and heat, so that the same law holds good through- 

 out, and thus enables us to connect the phenomena of sensation imiversaUy with 

 motion as its immediate external antecedent and exciting cause. Looking now 

 from the physical side of sensation to the mental, we shall find that the view _we 

 have just taken solves or dissipates many of the difliculties in which the question 

 has always seemed to be involved. First of aU, it makes the external cause and 



