Kno\vledge through our Senses. 451 



nielhod can be safely trusted alone. As Reid says, you may not 

 be able to tell exactly where you went astray, but if your path sud- 

 denly ends in a coal-pit you kiiow you have certainly gone astray. 



Suppose we follow each path separately first, before we tn to 

 find some integrating method which shall establish confidence in our 

 knowledge both of ourselves and of the objective world. 



You will not expect me in this short paper to describe the senses 

 or the nervous system in detail. Suffice it to say that we have a 

 system of nen-e centres and fibres, ramifying throughout the body, 

 and ending at its periphen in various complex modes. Within the 

 body, through this nervous system we become aware of a mass of 

 vague systemic sensations, none of which are in themselves of any 

 great intellective value, but which taken together are as important 

 to our mental view as the leaves of a forest are to the landscape. 

 At the surface of the bodv. one set of nerve-endings enables us to 

 perceive resistance; another, variations of temperature; another, 

 vai'ety of odour; another, of taste; a far more complex one. of 

 sound ; and the most exquisitely delicate of all gives us the world- 

 l)enetrating glories of sight. 



Xow. in all this there sems to be a strange incompleteness. Our 

 senso.s seem to have been thrown together at haphazard rather than 

 systematically co-ordinated to the end of knowledge. Indeed, at 

 first the\ seem entirely disparate. What, for example, is the com- 

 mon measure between sight and sound ? An approach to an answer 

 is found in the idea of movement or vibration. If matter f)e usually 

 found in masses, and if masses be composed of molecules, ami if 

 molecules may be considered as vortices in an all-pervading ether, 

 and if each molecule has its own characteristic internal movement, 

 tl.en the senses may be classified by saying that touch is massive, 

 hearing is molecular-massive, sight is molecular-etherial. and the 

 chemical senses of taste and smell are intramolecular. 



When we classify the senses so. we become conscious of wide 

 ga])s between them. An imaginar}- experiment, due (I believe) to 

 Dauve. will make this clear. Let us fancy we have a rod in aji 

 al)Solutely dark room, with preternatural means of revolving it at 

 any speed without limit. While the rod is at rest or moving slowly, 

 we can perceive it by touch only. At about 30 revolutions per 

 second we begin to hear it as a low musical note, rising through the 

 scales as the vibrations increase. Then it passes through shrillness 

 into silence, and after a pause, when it reaches, say, 300 billions of 

 revolutions per second, we begin to see it as a dull red light, passing 

 through all the .spectral colours, till our eyes lose it in the ultra- 

 violet rays. A further long pause, and we can conceive the vibra- 

 tions becoming so rapid as to affect intra-molecular movements, and 

 we might smell and taste the presence of the rod. — smell an<l taste 

 being perhaps as contiguous as touch and hearing. 



What about the gaps in this arrangement? Is there room for 

 other senses between hearing and sight, or between sight and smell? 

 And might not such other senses give us a totally different world? 

 Tndeeil, may we not suspect that some animals do possess other 



