250 Mr. T. Smith's Investigation of certain Phcenomena of 



ception in general, the uncertain state of our knowledge of 

 any function of sight beyond the mere formation of the image 

 on the retina, will, I trust, be deemed an apology for the mi- 

 nuteness of research and detail into which I have entered. 

 My wish has been to advance nothing which is not founded on 

 accurate observation, or experiment and legitimate induction. 

 In entering upon the investigation, it is of much importance 

 to form a correct conception of the optical relations of the 

 eyes at the time of making the experiments, and of the several 

 objects concerned in them. For this purpose, and to make 

 the phaenomena themselves better understood, a diagram will 



be useful. Let R and L, represent the right and left eyes; 

 P a distant point to which they are both directed; S a 

 narrow slip of white paper placed vertically between that 

 point and the eyes, and about ten or twelve inches from the 

 latter : F the flame of a lamp or candle near the right eye, and 

 so placed that rays from it may enter that eye freely, while 

 they are excluded from the left by an intervening obstacle 

 E G ; and F' an equal flame placed near the left eye. 



By the principles of optics, we know that straight lines 

 drawn from the objects through the optical centres of the eyes, 

 viz. c and c/, will touch those parts of the retina in each eye 

 on which the several images fall. Hence ef represent the 

 place of the image of F in the right eye; e' f that of the 

 image of F' in the left; m n and m' n' the places of the images 

 of S ; and o and o' the parts where the light from F and F' 

 would strike, if not prevented by the screen E G. 



It is a law of vision, that objects are perceived in the direc- 



