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just in the manner of that jn a camera obscura. The 

 rajs of light reaching from the surface of bodies to the 

 eye, variously penetrate the coats and humours of it, 

 , and paint on the bottom of the eye the images of the 

 things which \ve see. This is communicated by the 

 optic nerve to the brain, and then the perception, 

 which is properly Sight, follows : but the eye has 

 many advantages above a camera obscura ; not only as 

 it can be moved various ways by the help of its mus- 

 cles, but also as the pupil by the help of the iris, is 

 instantly either dilated or constringed according to the 

 degree of light. The eye likewise accommodates itself 

 to the various distances of the objects, the bottom of 

 the eye approaching to or receding from the crystalline 

 humour, as the object is nearer or farther off. 



8. Sound is a tremulous motion of the air, produced 

 by the stroke or collision of bodies. Hearing is per- 

 formed in the following manner : the undulating air 

 enters the outward cavity of the ear, and then strikes 

 upon the drum, from which the motion is communicat- 

 ed to the little bones within, and the air contained in 

 the inner cavity ; this, by means of the nerve, con. 

 veys it to the brain, and then follows the perception 

 which we term Hearing. 



9. The fine effluvia which spread every way from 

 cdorous bodies, ascending with the air into the nostrils, 

 variously twitch the filaments of the olfactory nerve?, 

 according to the variety of their natures. When this 

 motion is by those nerves communicated to the brain, 

 the perception follows which is called Smelling. 



10. It was observed before, that the surface of the 

 Tongue is filled with small papillae, which are no other 

 than fine ramifications of the gustatory nerve. These 

 are variously moved by the particles of meat and 

 drink; and this motion being by that nerve transmitted 

 to the brain ? that perception arises which we stile 

 Tasting, 



