or NATURAL HISTORY. 185 



tprnal bodies. By this fenfe we acquire the ideas of hard- 

 neis and foftnefs, of roughnefs and imoothnefs, of heat and 

 cold, of prelTure and weight, of figure, and of diftance. The 

 fenfe of touch is more uniform, and liable to fewor decep. 

 tions, than thofe of fmelling, tafting, hearing, and feeing ; 

 becaufe, in examining the qualities of obje£ls, the bodies 

 themfelves muft be brought into actual conta£l with the or- 

 gan, without the intervention of any medium, the varia« 

 tions of which might miflead the judgment. 



OF SEEING. 



OF all the fenfes, that of feeing is unqueflionably the no* 

 bleft, the moft refined, and the moft exteniive. The ear in^ 

 forms us of the exigence of objeiSts at comparatively fmall 

 diftances ; and its information is often imperfecl and falia-t 

 cious. But the organ of fight, which is moll admirably con?^ 

 {lru<5led, not only enables us to perceive thoufands of objects 

 at one glance, together with their various figures, colours, 

 and apparent pofitions, but, even when unarmed, to forn; 

 ideas of the fun and planets, and of many of the fixed flars ^ 

 and thus conne6ls us with bodies fo remote, that imagina^ 

 tion is lofi: when it attempts to form a conception of their, 

 immenfe magnitude and diftances. This natural field of 

 vifion, however, great, has been vaftly extended by the in- 

 vention of optical inflruments. When aided by the telef-? 

 cope, the eye penetrates into regions of fpace, and per- • 

 ceives ftars innumerable, which, without the afliftance of art, 

 would to us have no exiftence. Our ideas of the beauty^ 

 magnitude, and remotenefs or vicinity of external objects, are 

 chiefly derived from this delicate and acute inflrumcnt of 

 fen fat ion. 



Before proceeding to the peculiarities of vifion, and the 

 general properties of light, we fhall give ?. fhort defcription 

 of the flrutlure of the eve. 



