1855.] 



THEORY OF VISION. 



347 



some light implement, such as a garden trowel, with the assis- 

 tance of the hand. In removing the earth strict atten- 

 tion should be paid to any small objects contained in it : as 

 the practice of the Indians of this continent, as well as of 

 most other savage races, of burying weapons, implements, and 

 personal ornaments with the dead is well known. The better 

 to avoid any injury to the more essential parts, it is advisable, 

 where it can be done without great inconvenience, to pursue 

 the final jjrocess of laying bare the skeleton, by proceeding 

 from the feet towards the head. The bones ought not to be 

 attempted to be removed from the inclosing soil when they in- 

 dicate the slightest fragility, until the earth has been cautiously 

 removed all round them, so as to admit of their being lifted 

 out. Where the skull has been fractured, or any of the bones 

 of the fece are crushed or displaced by the pressure of the earth, 

 every fragment, however small, should be carefully collected ; ' 

 and if the soil has been damp, or the bones are rendered soft 

 by moisture, they should be exposed to the sun, before being 

 wrapped up in paper. 



Care should also be taken to note all the circumstances at- 

 tendant on the discovery, which are likely to throw any light 

 on the characteristics of the race, their mode of sepulture, or 

 their arts, customs, or habits. Nothing should be trusted to 

 memory, but all the facts noted at the moment and on the spot. 

 Some of the most important of the facts to be obseiwed and 

 noted down are : The position of the body, whether lying at 

 full length, on the back or side, or with the knees bent or 

 drawn up ; also the direction of the body, and position of the 

 head in relation to the points of the compass. 



Nest the nature and relative position of any relics, such as 

 urns, implements, weapons, &c., should be carefully noted ; 

 and among such, particular attention is to be paid to animal 

 remains, such as the bones and skulls, horns or teeth, of beasts, 

 birds and fishes. It is a common fashion among savage tribes 

 to hold a burial feast over the grave of the dead, and such 

 relics may tend to throw considerable light on the habits of the 

 people, as well as on the period to which they belong. 



In transmitting ancient skulls, they should be first wrapped 

 up in paper, — an old newspaper will be found the most suita- 

 ble for the purpose. Where there are detached pieces each 

 should be put up in a separate wrapper. The whole may then 

 be put in a box with a little hay, which furnishes an inclosure 

 sufiiciently clastic to protect the most fragile bones from in- 

 jury during carriage. 



As such relics loose much of their value when the locality 

 and circumstances of their discovery are unknown, it is ex- 

 tremely desirable not oidy to attach to each skull, package of 

 bones, or acconipanj'ing relics, the name and description of the 

 locality where they have been found, but also as soon as pos- 

 sible to mark this neatly and indelibly upon the object itself. 

 Where more than one skull has been procured, and any of 

 them are in a fragmentary state, it is scarcely necessary to add 

 that the utmost care should be taken to keep the several por- 

 tions of each skull distinct from the others; as even whore it 

 may be possible afterwards to separate them, this must always 

 be attended with much additional labour, and generally with 

 some uncertainty. It may be further added that in no case 

 should a skull, or other relic of this class, be deposited finally 

 in a collection, without a distinct note of the locality of its dis- 

 covery being marked on it in a durable manner. 



I). W. 



On the Extent to which the received Theory of Vision re. 

 quires us to regard the Eye as a Camera Obscnra. 



BY GEORGE WILSON, M.D., F.R.S.E. 



Director of the Industrial Museum of Scotland, and Professor of 

 Tcchnolofjrj in the Unirersiti/ of Edinburgh. 



In the last i.ssue of the Transactions of the Royal Society of 

 Edinburgh,* a highly interesting paper bearing the above title 

 furnishes views on the structure and function of the eye in 

 relation to vision, which will tend to modify to a very consi- 

 derable extent the views of physiologists on this important 

 subject. Dr. Wilson takes it for granted that, according to 

 the received theory of vision, the eye of man, as well as that 

 of most of the lower animals, is regarded as essentially realiz- 

 ing, during the performance of its function of .sight, the con- 

 dition of a darkened chamber, or camera ohscura. In .sup- 

 port of this assumption of the existing views of physiologists, 

 he cites one of the highest living authorities. Professor Midler, 

 and then proceeds to say : — " Thus far, then, there does not 

 appear to be room for two opinions concerning the internal 

 darkness of the human eye being a condition of perfect sight. 

 Rut recent discoveries require us to look at the theory of 

 vision from an opposite point of view. It is now beyond 

 question, that even in the darkest human eye, there is reflec- 

 tion through or across its chamber, from the surface of the 

 retina, as well as from that of the choroid ; and the observation 

 is a very old one, that in a large number of animals, a part, 

 and sometimes the whole of the retinal surface is covered, or 

 replaced by a reflector rivalling in brilliancy a sheet of polished 

 silver. 



" That the eyes of living men and women emitted light, 

 and shone like those of the cat, had been occasionally 

 noticed and recorded from an early time, but the pheno- 

 menon was supposed to be~ an exceptional, and indeed 

 very rare one, and was either credulously magnified into a 

 highly marvellous occurrence, or despised as of questionable 

 accuracy, and of little real significance. In (or about) 1847, 

 however, Mr. Gumming, an English medical practitioner, 

 pointed out that the phenomenon in question might be wit- 

 nessed in every human eye, if looked for in the right way ; and 

 a little later and independently, Briicke made the same dis- 

 covery in Germany, through the curious circumstance, that 

 occasionally when looking through his spectacles, at the face 

 of another, he saw his neighbour's eye glare like a cat's. 



" The demonstrability of the proposition, that the eye is not 

 a camera obsciira, depeiuls upon the fact, that when rays of 

 light enter the eye, and fall upon its back wall, as many of 

 them as are reflected from the retina, or from the choroid bo- 

 hinil it, will exactly retrace their course, and pass out through 

 the pupil to the luminous body or illuminated object from 

 which they came. Thus the diverging rays of a g-as-flame arc 

 converged by the reft-acting media of the eye, to a focus upon 

 the retina, where they unite to produce a picture, and there- 

 after in great part traverse that membrane and fall upon the 

 choroid. If from either of these membranes rays arc reflected 

 (and for the sake of simplicity, we may, for the present, limit 

 ourselves to the retina, which is the more powerful reflector of 

 the two), they will follow in a revci-sed direction, the very 

 eoui-se which they took in reaching that membrane, and return 

 to the ga.s-flame, producing there an image of the picture on 

 the retina, so that the retteeted image of the flame i.s placed 

 upon, and coincides in size and position with the actual flame. 



Ti-an.saction« of the Royiil Society of E(linburi;li, Vol. XXI., Part IF. 



