X CONTENTS OF VOL. II 



— Distribution of the nerves of touch, taste, smell, and sight, to sensitive 

 surfaces — Distribution of the nerves of hearing different — Laws of sonorous 

 vibrations — Period of vibration constant for the same string — Pitch of note 

 constant for the same string — One string may set another vibrating — Action of 

 sound on the nerves of the ear — Tone of sound : how produced — Why do the 

 secondary vibrations, or overtones, combine with the fundamental into a re- 

 sultant sound ? — The combination or distinction maj' be due to habit — With 

 practice overtones may be distinguished — Sight and hearing are the most 

 intellectual, and the only sesthetic senses — Music produces a more intense 

 feeHng than visual beauty, because the ear loses no time in combining 

 impressions. 



Note A : Nerves of Special Sensation : — Opinion of distinct nerves for distinct 

 colours — Reasons against this — No special nerves of taste, nor of heat — The 

 kind of sensation depends not on the nerves, nor on the ganglia, but on the 

 organ of sense — Sensations of light due to pressure, and to an electric current. 



Note B : Colours and the Laws of their Combination : — Difference between sen- 

 sations of sight and of the other senses — Meaning of ligJit and of radiance — 

 Heating and chemical effects of radiance — Eadiance consists of undulations — 

 Rays of different wave-lengths are mixed together in the sunbeam — Their sepa- 

 ration by the prism — The places of brightest light, of greatest heating power, 

 and of greatest chemical power, do not coincide — Different rays have different 

 colours — Succession of colours — Difference of colour is a physiological fact, and 

 analogous not to tone but to pitch in sound — The octave in sound and in colour 

 ■ — The series of colours in the spectrum is circular, and the opposite colours are 

 complementaries — How to combine colours — Whites produced by the comliina- 

 tion of different pairs of complementaries are optically different — All colours 

 except white are in the spectrum — Black — Grey — BroAvn — Result of combining 

 two colours not complementary is to form compound colours visibly like simple 

 ones, but optically different — No distinction of primaries and secondaries in 

 any physical sense, but there may be in a physiological sense — Further mathe- 

 matical considerations — Wave frequency — A colour and its octave are 360" 

 apart on the circle — We might expect complementaries to be 180° apart — Dis- 

 crepancy of observation and theory — How accounted for — All the rays are not 

 equally bright to our eyes — Possibility of giving a formula for any tint — Scien- 

 tific principles of harmonious colouring Pp. 92 — 116 



CHAPTER XXXVL 



PERCEPTION. 



The problem, how sensations give rise to perceptions — Perception is more than 

 cognition : it is the referring of sensations to their sources, the sources being 

 present in time — A perfectly accurate definition is impossible — Perception is an 

 inference — The same act may be the one or the other, according to circum- 

 stances — The subject has been complicated by extraneous questions — Perception 

 and the cognition of space are distinct, but have been confounded — We cognise 

 space before we perceive objects in it — Cognition of two sensations as separated 



