HERMANN l.l'BWIG FKK1MNANU HKLMHOLTZ. 



own frame of mind Othera might study the conditions under which an impulse 

 it propagated along a nerve, and might suppose that while doing so they were 

 studying actuations, but though such a procedure leaves out of account the 

 very oaymrin of the phenomenon, and treats a fact of consciousness as if it 

 were an electric current, the methods which it has suggested have been more 

 f.Ttilf in results than the method of self-contemplation has ever been. 



But the best results are obtained when we employ all the resources of 

 physical science so as to vary the nature and intensity of the external stimulus, 

 and then consult consciousness as to the variation of the resulting sensation. 

 It was by this im-thod that Johannes Muller established the great principle 

 that the difference in the sensations due to different senses does not depend 

 upon the actions which excite them, but upon the various nervous arrange- 

 ments which receive them. Hence the sensation due to a particular nerve may 

 \arv in intensity, but not in quality, and therefore the analysis of the infinitely 

 lious states of sensation of which we are conscious must consist in ascertain- 

 ing the number and nature of those simple sensations which, by entering into 

 consciousness each in its own degree, constitute the actual state of feeling at 

 any instant. 



If, after this analysis of sensation itself, we should find by anatomy an 

 apparatus of nerves arranged in natural groups corresponding in number to the 

 -lementa of sensation, this would be a strong confirmation of the correctness 

 of our analysis, and if we could devise the means of stimulating or deadening 

 each particular nerve in our own bodies, we might even make the investigation 

 physiologically complete. 



The two great works of Helmholtz on Physiological Optics and on the 

 Sensations of Tone, form a splendid example of this method of analysis applied 

 to the two kinds of sensation which furnish the largest proportion of the raw 

 materials for thought. 



In the first of these works the colour-sensation is investigated and shewn 

 to depend upon three variables or elementary sensations. Another investigation, 

 in which exceedingly refined methods are employed, is that of the motions of 

 the eyes. Each eye has six muscles by the combined action of which its 

 angular position may be varied in each of its three components, namely, in 

 altitude and azimuth as regards the optic axis, and rotation about that axis. 

 There is no material connection between these muscles or their nerves which 

 would cause the motion of one to be accompanied by the motion of any other, 



