306 Animal Life and Intelligence. 



raised to the level of sensations, in so far as they are 

 recognized and discriminated. 



Let us now glance at some of the differences in quality 

 recognized in sensation. First, we have the broadly dis- 

 tinguished groups of touches and pressures, temperature- 

 sensations, tastes, smells, sounds, sights, muscular sensa- 

 tions, and organic sensations from internal parts of the 

 body. And then, within each of these groups, there are 

 the more or less delicate and distinct shades of quality, 

 well exemplified in vision by the different colour-sensations, 

 in hearing by notes of different pitch, and in smell by the 

 varieties of scents and odours. Many of those sensations, 

 moreover, which are apparently simple, are in reality 

 compound. There are differences of quality in the note A 

 as sounded on a violin, a piano, and a flute ; and these 

 differences are due to different admixtures of overtones, 

 which fuse with the fundamental tone and alter its timbre. 

 So, too, with vision. The sensation given by a white disc 

 is a compound sensation, due to waves of different period, 

 which separately would give sensations of colour. Sensa- 

 tions, then, differ in quality. 



They also differ in quantity or intensity. This needs 

 little illustration. As evening falls, the sight-sensations 

 derived from the surrounding objects grow more and more 

 feeble. They may remain the same in quality, but the 

 quantity or intensity gradually diminishes. So, too, in 

 music, the pianos and fortes give us differences in intensity 

 of sound-sensations. 



Sensations also differ in duration. The stimulation 

 may be either prolonged or instantaneous. Two or more 

 sensations may, moreover, be simultaneous or successive. 

 Just as they may be either similar or different in quality 

 and in intensity, so they may be either simultaneous or 

 successive in time. Simultaneous sensations are best 

 exemplified in vision and through touch ; successive sensa- 

 tions are given most clearly by the sense of hearing, 

 through which we recognize a sequence of sounds. 



And then, again, sensations not only differ in time, but 



