452 THE SENSORIAL FUNCTIONS. 



which no light is allowed to enter, except what 

 is admitted through a small hole in a shutter, 

 so as to fall on the opposite side of the room. 

 It is evident that each ray will, in that case, 

 illuminate a different part of the wall, and that 

 the whole external scene will be there faith- 

 fully represented ; for the several illuminated 

 points, which constitute these images, preserve 

 among themselves the same relative situation 

 which the objects they represent do in nature, 

 although with reference to the actual objects 

 they have an inverted position. This inversion 

 of the image is a necessary consequence of the 

 crossing of all the rays at the same point; 

 namely, the small aperture in the shutter, 

 through which they are admitted. 



One inconvenience attending the limiting of 

 the illumination of each point of the wall to that 

 of a single ray, in the mode last pointed out, is 

 that the image produced must necessarily be 

 very faint. If, with a view of remedying this 

 defect, the aperture were enlarged, the image 

 would, indeed, become brighter, but would 

 at the same time, be rendered more indistinct, 

 from the intermixture and mutual interference 

 of adjacent raj^s ; for all the lines would be 

 spread out, the outlines shaded off, and the whole 

 picture confused. 



The only mode by which distinctness of image 

 can be obtained with increased illumination, is 



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