CHAMBERS'S INFORMATION FOR THE PEOPLE. 



therefore pure feelings of muscularity. The use of 

 touch in connection with those perceptions is to 

 give marks or starting-points, and a definite course 

 m making the sweep. Simple Length is motion 

 in one direction. Surface implies movements 

 along and across, while Solidity needs us to sweep 

 in three different directions. The hand, with its 

 plurality of fingers, each distinctly sensitive, has 

 a peculiar advantage in taking in the different 

 dimensions of bodies. By the span of the hand, 

 we appreciate Length ; by the extended hand, we 

 feel a Surface ; and by combining this with the 

 thumb, we are aware of what distinguishes a Solid. 

 Distance, Direction, and Situation are got at in a 

 similar manner. 



Hearing. 



This sense is more special and local than the 

 foregoing, but agrees with it, in being a mechanical 

 sense, as distinguished from the two chemical 

 senses Taste and Smell The Sensations of 

 sound may be divided into three classes : i. The 

 general effects of sound, as determined by Quality, 

 Intensity, and Volume or Quantity. By quality 

 is meant the character of sounds, as agreeable or 

 disagreeable in themselves, like sweet and bitter 

 in taste. The pleasing effects of a pure sound are 

 expressed by the terms sweet, mellow, rich. Inten- 

 sity or loudness is of the nature of pungency, as 

 already explained in the other senses, agreeable 

 within limits, painful beyond. Volume means the 

 sound coming from a sounding mass of great sur- 

 face or extent the waves of the sea, the discharge 

 of thunder, the shouts of a multitude. 2. Musical 

 Sounds. The fundamental property of sound in 

 relation to music is pitch. Sounds agreeing in 

 pitch, or formed of an equal number of vibrations, 

 are said to be of the same musical note ; and a 

 series of different pitches, or notes, drawn up with 

 definite intervals, are the notes of the musical 

 scale. The waxing and waning of sound is one 

 of the effects introduced into musical execution, 

 owing to the power it has to excite a very strong 

 and pleasurable emotion. Complexity gives occa- 

 sion to the two effects of discord and harmony 

 the one painful, and the other, acutely pleasur- 

 able Clearness may attach to sound as to any 

 other expression. 3. Sounds that serve in the per- 

 ception of the outer -world. The discrimination 

 between sounds as coming from different materials, 

 is an important property of the ear, rendering it 

 an instrument of useful knowledge. The ring of 

 a shilling and a sovereign, or the voices of two 

 different persons, are clearly distinguished. Direc- 

 tion is purely acquired, and the concurrence of 

 the two ears is a powerful aid in indicating it. So 

 is the distance of sounds. The articulate form 

 relates to the effect produced by the sounds issuing 

 from the human voice, as modified by the con- 

 figuration of the mouth in the act of uttering 

 them. 



Sight. 



A great many difficult questions are involved in 

 the processes of vision. The adaptation of the eye 

 to sight at different distances, the theory of single 

 vision with two eyes elucidated by Wheatstone, 

 the inventor of the stereoscope the seeing objects 

 erect by means of an inverted image on the eye, 

 have been long discussed, and are now tolerably 

 well understood. 



310 



The Sensations of sight are in part optical 

 purely, and in part a combination of the optical 

 with the muscular. 



Mere light, as in the diffused solar radiance, is 

 one of the most powerful among our simple sensa- 

 tions. In clear, strong sunshine, freshly encoun- 

 tered, there is a massive influence of pleasurable 

 elation, more endurable than most other pleasures 

 of the same strength. Colour is an effect dis- 

 tinct from mere light and shade, and would 

 seem to give a more pungent stimulus to the 

 eye, which would render it less soft and endur- 

 able, but for the opportunity presented of making 

 up harmonies, from which a new pleasure takes 

 its rise. Lustre is caused by colour seen through 

 a transparent film or covering, and produces a 

 fresh, rich, luxurious feeling, lying at the founda- 

 tion of our delight in many objects of nature and 

 works of art. 



The complex sensations of sight are those that 

 involve the movements of the eyeball with the 

 impressions of light. Motion, as appreciated by 

 the eye, is a compound of light and movement ; 

 the eye must be moved to follow the object, and 

 the resulting sensation has therefore a muscular 

 element. Hence all the feelings due to the opera- 

 tion of muscles, and all that discrimination of 

 differences of range and pace necessary to external 

 perceptions, are generated in the processes of 

 seeing. Distance is recognised through the chang- 

 ing adjustment of the eye, but we must have 

 experience in order to know that one adjustment 

 means near, and another far. Form is perceived 

 entirely by the muscular portion of the eye ; inas- 

 much as outline can only be taken in by carrying 

 the vision successively along the track marked 

 out. A round form is impressed by one set of 

 movements, a square form by a different set. 

 Apparent magnitude is also determined by the 

 muscular sweep of the eye. Solidity results from 

 taking in varying distance along with the visual 

 expanse. To recognise surface, or two dimensions, 

 the movement of the eye right and left, up and 

 down, might suffice, if the object is not placed 

 slanting, but a third dimension always implies 

 varying distance. A block of stone is a compound 

 of form, visual expanse, and unequal distance from 

 the eye. 



Thus the eye repeats all those acquirements 

 made through combined Touch and Muscularity, 

 and from the greater persistence of impressions 

 of vision, retains them with more vividness and 

 tenacity. This renders sight the intellectual sense 

 by pre-eminence. For the purposes of discrimina- 

 tion and of identification of natural things, and 

 also for the storing of the mind with knowledge 

 and thought, the sensations of objects of sight are 

 available beyond any other class. 



THE APPETITES. 



The appetites are a select class of our sensations 

 and feelings, defined as the cravings produced by 

 the recurring wants and necessities of our bodily 

 or organic life. The taking in of nourishment, the 

 ejection of what is formed to be thrown out, the 

 supply of air, the alternation of exercise and rest, 

 are forced upon us by strong uneasy sensation. 

 The property of periodic recurrence, which is the 

 main distinction of an appetite, is in no case more 

 strikingly exemplified than in Sleep. After a 



