HARDWICKE'S SCIENCE GOSSIP. 



31 



THE HUMAN EYE. 



npiIE publishers of a work just issued on " The 

 -*~ Wonders of the Human Body," * translated 

 from the Erench, give the following reasons for 

 doing so. " There is an increasing tendency in the 

 present day to make common property of special 

 knowledge. Even such information as formerly 

 belonged to certain professions alone is, at least in 

 its rudiments, becoming more 'generally diffused ; 

 and on the part even of those professions the ten- 

 dency is recognized as within reasonable bounds 

 deserving of encouragement. To take ' the human 

 body ' as an illustration, medical men find that the 

 useful feature of their art is facilitated by the dis- 

 semination of information regarding its structure 

 and functions. On the other hand, the public daily 

 see more and more clearly that 'prevention is better 

 than cure,' and that to prevent derangements of 

 the wonderful machine, with the guidance of which 

 each individual is entrusted, more acquaintance 

 with its mechanism and laws of normal action is 

 indispensable. Apart from its utility, a knowledge 

 of anatomy and physiology is gradually becoming a 

 necessary part of a liberal education. To meet 

 these requirements the publishers now present this 

 translation from the French of a book which, in the 

 original, has attained to great popularity," &c. 



Without attempting to institute comparisons 

 between this book and others on the same subject 

 which preceded it, we will content ourselves with 

 an extract from the chapter on "The Human Eye." 

 "As regards the distance at which man can distin- 

 guish objects, he is less gifted than many other 

 animals; but in every other respect his visual powers 

 are at least equal to that of inferior beings. We 

 know very little of the sensations produced in ani- 

 mals by colours ; it seems probable that they have 

 a relative perception of them to a certain extent, as 

 the sight of red irritates the bull, for example ; and 

 we know that birds of prey from a great height in 

 the air distinguish the colour as well as the form of 

 a lark or quail hiding in the ploughed fields, although 

 it so closely resembles that of the soil. But if we 

 should suppose them endowed with sensitive facul- 

 ties, useless within the limits of their instinct, 

 could we find anything in animals more perfect than 

 the organs to which man owes the prodigies of 

 painting? We must, however, distinguish here 

 between that which pertains to the visual apparatus 

 and that which proceeds from the intellect. The 

 eye perceives the tints which nature offers in almost 

 infinite variety ; the mind compares them, and re- 

 cognizes the elementary colours of which they are 

 composed ; the eye reflects in turn the model, the 



* "Wonders of the Human Body," from the French of 

 A. le Pileur, M.D. Illustrated by forty-five engravings by 

 Leveille. London : Blackie & Son. 



palette, and the picture; the mind perceives the 

 relation of shades, and combines them in such a 

 manner, that by mingling or contrasting them such 

 a result is produced as conforms to the first im- 

 pression; but in order that an artist may judge 

 whether red or blue predominates in a violet tint, 

 in order to appreciate the shade, the retina must 

 transmit it to the brain iu its purity. 



"At the manufactory of the Gobelins we see the 

 wools used in the fabrication of the tapestries 

 arranged according to their shades. The number 

 of these shades exceeds 23,000, and yet when we 

 compare two approximate shades we distinguish 

 them with facility, and perceive the interval which 

 separates them. 



"The people who live in the country, seamen, and 

 especially men living in a savage state, generally 

 have sharper sight than the residents of cities. May 

 not the habit of seeking to distinguish objects at a 

 distance give the eyes a power which is not acquired 

 when they always act within a limited horizon? 

 Without assimilating exactly the effects of exercise 

 on the eye to those which result from exercise of a 

 muscle, we are justified in thinking that an almost 

 incessant accommodation to great distances must 

 influence the eye in that respect, and if, as is very 

 probable, the accommodation takes place by the con- 

 traction of the muscular fibres, the explanation of 

 the increased range of the eye from exercise is very 

 simple ; but facts are wanting which verify and 

 measure this increase in individuals. There is no 

 doubt, however, that men from whom the horizon is 

 habitually distant distinguish certain objects at a 

 point where they are confused to other persons, 

 although within the reach of their vision. 



" A ship appears on the horizon, a man unac- 

 quainted with the sea can hardly distinguish the 

 sails of this white cloud springing from the waters ; 

 but a sailor will tell you that it is a brig, or a three- 

 master, a war vessel or a merchant ship, and often 

 he will even come at its tonnage, its lading, its na- 

 tionality, and its name. The Arab and the European 

 in the midst of the sands of Sahara see on the hori- 

 zon an object, which to the European is only a black 

 point without appreciable form ; the Arab sees a 

 camel distinctly, and declares that it is at such or 

 such a distance, without ever being deceived. 



"The inexperienced mountain traveller sees before 

 him a chaos of slopes and abrupt walls, of elevations 

 and windings, among which he can distinguish 

 neither route nor practicable passage ; but the 

 mountaineer sees at once the accessible points, and 

 the turns which he must take to reach the summit 

 of the apparently impassable barrier. This proves 

 not that the sailor, the mountaineer, and the Arab 

 have sharper sight than the strauger to their coun- 

 try ; but that they have learned to know the signi- 

 fication of such and such details of form, such a 

 particularity of colour, and the like, which are for 



