PHYSICAL andLITERARY. s| 



But, fo far have his intentions been difap- 

 pointed hitherto, that few phyfical writers 

 feem to comprehend diftinftly the hints 

 which he has left concerning the manner of 

 inflexions *i and none, as far as I know, hasi 



advanced 



* When any opaque body is held at the dlftance of three 

 or four inches from the eye, fo that a part of fome more 

 tiiftant luminous objedt, fuch as the window or the flame of 

 a candle, may be feen by rays paffing near its edge : If 

 another opaque body, nearer to the eye, be brought acrofs 

 from the oppofite fide ; the edge of the firft body will feem 

 to fwell outwards and meet the latter, and, in doing fo, will 

 intercept a portion of the luminous objedt that was feea 

 before. .... 



" This phrenomenon has been rafhly afcribed to the inflexion 

 (of light, by fuch as underftood not thoroughly the nature of 

 inflexion, nor obferved accurately the circumftances of the 

 faa. 



■ .Let AB reprefent the luminous objeft (Tab. iii. Fig. 5.) 

 to which the fight is direfled, CD the more diftant opaque- 

 body, GH the nearer, and EF the diameter of the pupil j 

 join ED, FD, EG, FG, and produce them till they meet 

 AB in K, N, M and L : It is plain, that the parts AN," 

 MB of the luminous obje6l cannot be feen. But, taking any 

 point a between N and K, and drawing ciDd ; iince the 

 portion ^F of the pupil is filled with light flowing from 

 that point, it muft be vifible : any point b between a 

 and K muft fill /F a greater portion of the pupil, and' 

 therefore muft appear brighter. Again, any point c between 

 b and K muft appear brighter than b, becaufe it fills a 

 greater portion oF with light. The point K itfelf, and every 

 other point in the fpace KL, muft appear with comp'eat 



lu:!lre ; 



\ 



