250 ON THE SENSES. 



only to show tliat we should undertake an impossibility did we aim to commu- 

 nicate to the novices of science a complete comprehension of the mechanism of 

 the action of the senses. We fear, indeed, that for some of the teachings of the 

 theory of physical sensation, which are clear enough to the learned, it will be 

 difficult to find in the circuit of popular ideas pencil or colors with which to 

 trace a clearly comprehensible image. No doubt, indeed, that at the present 

 day, when both fashion and profit conspire to popularize the treasures of science, 

 there may be found limners who, in comparison with effectiveness, consider any 

 plain portraiture of the objects of sober science quite a secondary affair ; but we 

 eschew all afHliatiou with artists of this sort ; we willingly exchange the cheap 

 glitter of the parade for the honor of standing as a sentry before the sanctuary 

 of science. There is a vast deal in the sphere of the physiology of the senses, 

 which may be plainly translated into the language of the laity of science, and 

 which is of the more interest to them as false representations and notions are 

 deeply rooted and widely prevail in the ideas and expressions of mankind. 



How little do men understand the operations of their senses, how little are 

 they qualified to form a right conception of the nature and import of a simple 

 sensation, pertain to whichever of the senses it may, so as to separate, on the 

 one hand, this bare sensation from the multifarious impressions which insensibly 

 combine with it, and to distinguish, on the other hand, the qualities of the sen- 

 sation from the properties of the external objects and incidents which occasion 

 it. One or two examples will substantiate this charge, and many a reader, we 

 are convinced, will with surprise hear that named an error which he holds to 

 be unquestionable truth and the result of direct observation. You hear the 

 sound of a string which is struck, and speak of the " resounding string ;" you 

 see the leaves of the trees and designate the green color as a property of the 

 leaves ; you taste sugar and impute to the sugar the sweet taste : these are all 

 errors ! The string only vibrates — it does not sound ; the sound originates in 

 yourself, is the peculiar and no further to be explained sensation which arises 

 when the vibrating string has by its oscillations set in motion the particles of 

 air, a motion which these particles convey to the tympanum of the ear, this in 

 turn to the small bones of that organ, these to the fluid of the so-called laby- 

 rinth, and this to the extremities of the auditory nerves, when it is propagated 

 through these nerves by the unknown movement which we have designated 

 above as " a current" to the brain, and by a suitable adjustment of that appa- 

 ratus produce the condition of our sentient nature of which we are conscious 

 as sound. The original vibrations determine the character of the sound, but 

 have nothing in common with it. The same is the case with the green color of 

 leaves: the leaves are not green; they but possess the quality of producing 

 the sensation which we term green, without knowing what green is, except that 

 it depends on the presence between the eye and the leaf of an impalpable fluid 

 or ether whose ti-emulous palpitations are propagated to the organ of sight in 

 the form of waves. When a wave of this sort strikes upon the extremities of 

 the nerves in the back of the eye, that unknown current is again produced in 

 the appropriate filaments, and this it is which calls into being in the brain the 

 sentient condition which we call the sensation of light. This wave of the 

 ethereal particles in vibration has, like the waters of the agitated sea, a deter- 

 minate length, a determinate velocity, which science has measured, though the 

 ether itself be wholly inscrutable. Were the waves which proceed from the 

 leaf longer or shorter, were the velocity of the vibrations greater or less, they 

 would excite in the perceptive fliculty, through the nerves, a differently modi- 

 fied sensation which we should designate as a red, blue or yellow color. This 

 then is the first striking error, that each of us considers the qualities of his own 

 sensation to be the qualities of the external object or incident which is the 

 cause of the sensation. It is an error hard to be eradicated, as it is entwined 

 with our habits both of thought and speech, and finds countenance not only in 



