168 



SENSORIAL FUNCTIONS. 



whole of this extent must be pictured on the diameter of 

 half an inch at the same instant, otherwise it could riot be 

 seen at the same view. 



508. The Rev. Dr. Dick, in his Christian Philosopher," 

 a work which should be read by all mankind, has calcu- 

 lated that a portion of the castle of Edinburgh, equal to 

 fi\ e hundred feet long and ninety in height, occupies on the 

 retina only the twelve hundred thousandth part of an inch, 

 when seen at a certain distance, and yet every part was 

 distinctly visible. What then might be the dimensions 

 of the picture of a fixed star on the same organ ? 



509. Dr. Roget, in his " Animal and Vegetable Physi- 

 ology," speaking of this organ, says : " Few spectacles are 

 more calculated to raise our admiration than this delicate 

 picture, which nature has, with such exquisite art, and 

 with the finest touches of her pencil, spread over the 

 smooth canvass of this subtle nerve ; a picture, which, 

 though scarcely occupying the space of half an inch in 

 diameter, contains the delineation of a boundless scene of 

 earth and sky, full of all kinds of objects, some at rest, and 

 others in motion, yet all accurately represented, as to their 

 forms, colors, and positions, and followed in all their 

 changes, without the least interference, irregularity, or 

 confusion. Every one of those countless and stupendous 

 orbs of fire, whose light, after travelling immeasurable re- 

 gions of space, at length reaches our eye, is collected on 

 its narrow curtain, into a luminous focus of inconceivable 

 minuteness ; and yet this almost infinitesimal point shall 

 be sufficient to convey to the mind, through the medium 

 of the optic nerve and brain, a knowledge of the existence 

 and position of a far-distant luminary, from which that 

 light has emanated. How infinitely surpassing all the 

 limits of our conception must be the intelligence and pow- 

 er of that Being who planned and executed an instrument 

 comprising within such limited dimensions, such vast pow- 

 ers as the eye, of which the perceptions comprehend alike 

 the nearest and most distant objects, and take cognizance 

 at once of the most minute portions of matter, and of 

 bodies of the largest magnitude." Bridgewater Treatise, 

 vol. ii., p. 476. 



