OF NATURAL PHILOSOPHY. 249 



motions susceptible of ocular examination, and has 

 been lately much improved on, and varied in its ap- 

 plication, by M. Savart, to whom we also owe a suc- 

 cession of instructive researches on every point 

 connected with the subject of sound, which may 

 rank among the finest specimens of modern experi- 

 mental enquiry. But the subject is far from being 

 exhausted ; and, indeed, there are few branches of 

 physics which promise at once so much amusing in- 

 terest, and such important consequences, in its 

 bearings on other subjects, and especially, through 

 the medium of strong analogies, on that of light. 



Light and Vision. 



(273.) The nature of light has always been involved 

 in considerable doubt and mystery. The ancients 

 could scarcely be said to have any opinion on the 

 subject, unless, indeed, it could be -considered such 

 to affirm that distant bodies could not be put into 

 communication without an intermedium ; and that, 

 therefore, there must be something between the eye 

 and the thing seen. What that something is, how- 

 ever, they could only form crude and vague con- 

 jectures. One supposed that the eyes themselves 

 emit rays or emanations of some unknown kind, by 

 which distant objects are as it were felt ; a singularly 

 unfortunate idea, since it gives no reason why 

 objects should not be equally well seen in the dark 

 no account, in short, of the part performed by light 

 in vision. Others imagined that all visible obj ects are 

 constantly throwing out from them, in all directions, 

 some sort of resemblances or spectral forms of 

 themselves, which, when received by the eyes, 



