WISDOM OF TIIiS DEITT. 



aqueous humour, m, n, and the crystalline humour 

 , p, and the vitreous humour, D, E, will be con 

 verged to a focus on the retina, and paint a dis 

 tinct picture, a 6 c, of the object ABC, in an 

 inverted position. The rays from the point A 

 of the object, after being refracted by the different 

 humours, will be brought to a point at a ; those 

 from B will be converged at b ; and those from 

 C ate; and, of course, the intermediate rays 

 between A B, and B C, will be formed between 

 a 6, and b c, and the object will become visible 

 by means of its image or representation being 

 painted on the retina, in all the colours and pro 

 portions which belong to it. If we take a bul 

 lock s eye, and cut off the three coats from the 

 back part, and put a piece of thin white paper 

 over that part, and hold the eye towards the win 

 dow or any bright object, we shall see the image 

 of the object depicted upon the paper, and in an 

 inverted position, as stated above. 



In order that we may more distinctly perceive 

 the wonders of vision, and the numerous circum 

 stances on which it depends, let us suppose our 

 selves placed on an eminence, which commands 

 a view of a variegated and extensive landscape. 

 Let us suppose ourselves stationed on Arthur s 

 seat, or on the top of Salisbury Crags, in the vi 

 cinity of Edinburgh. Turning our face to the 

 north-west, the city, with its castles, spires, and 

 stately edifices, presents itself to our view. Be 

 yond it, on the north and west, a beautiful coun 

 try, adorned with villas, plantations, and fertile 

 fields, stretches as far as the eye can reach, till 

 the view is bounded by the castle of Stirling, at 

 the distance of more than thirty miles. On the 

 right hand, we behold the port of Leith, the ship 

 ping in the roads, the coast of Fife, the isles of 

 Inchkeith and of May, and the Frith of Forth, 

 gradually losing itself in the German ocean. If 

 we suppose the length of this landscape to be 

 forty miles, and its breadth twenty-five, it will, 

 of course, comprehend an area of a thousand 

 square miles. 



The first circumstance which strikes the mind, 

 is the immense multitude of rays of reflected light 

 which flow, in all directions, from the myriads 

 of objects which compose the surrounding scene. 

 In order to form a rude idea of this infinity of 

 radiations, I fix my attention on a single object 

 I direct my eye to Nelson s monument, o the 

 Gallon hill. From the parapet at the top, a thou 

 sand different points send forth a thousand differ 



ent cones of rays, which, entering my eye, re 

 der the different parts of it distinctly visible, be 

 sides myriads of rays from the same points, 

 which flow in every other direction through the 

 open spaces of the atmosphere which surround 

 them. How many thousands of millions, then, 

 of different radiations, must be issuing forth 

 every moment from the whole mass of the monu 

 ment ! And if one object pours forth such a flood 

 of rays, how immense must be the number of ra 

 diations which are issuing from all the objects 

 which compose this extensive landscape ! My 

 riads of rays, from myriads of objects, must be 

 crossing each other in an infinity of directions, 

 so that the mind is confounded at the apparent 

 confusion which seems to exist in this immensity 

 of radiations ; yet every ray passes forward in 

 the crowd, in the most perfect order, and without 

 being blended or confused with any other ray, pro 

 duces its specific effect on every eye that is open 

 to receive it. But this is not all : these millions 

 of rays which flow from the minutest points of 

 the surrounding scene, before they can produce 

 the sensation of vision, and form a picture of the 

 landscape on the retina, must be compressed into 

 a space little more than one-eighth of an inch in 

 diameter, before they can enter the pupil of the 

 eye ; yet they all pass through this small aperture 

 without the least confusion, and paint the images 

 of their respective objects in exactly the same 

 order in which these objects are arranged. An 

 other circumstance demands attention. The 

 rays which proceed from the objects before me 

 are not all directed to the spot where I stand, but 

 are diffused throughout every point of the sur 

 rounding space, ready to produce the same effect, 

 wherever sentient beings are present to receive 

 them. Were the whole inhabitants of Edin 

 burgh placed on the sloping declivity of Arthur s 

 seat, and along the top of Salisbury Crags, and 

 were millions of other spectators suspended in the 

 surrounding atmosphere, similar sensations would 

 be produced, and a scene similar to that which 

 I now behold, would be depicted in every eye. 

 Amidst the infinity of cones of light, crossing 

 each other in an infinity of directions, no confu 

 sion would ensue, but every spectator, whose 

 eyes were in a sound state, would obtain a cor 

 rect view of the scene before him ; and hence it 

 happens, that, whenever I shift my position to 

 the right hand or to the left, other streams of light 

 enter my eye, and produce the same Cect Vt 



