" Experiments and Observations on the Propei-ties of Light." 7 



formed equally, whether the edge be parallel or perpendicular to 

 the aperture; though in the latter case they may for obvious 

 reasons be less distinct and conspicuous. 



It might indeed be fully admitted that the rays formmg the 

 white centre mav be in some respects under different conditions 

 from the ordinary rays, and that thus the fringes formed m them 

 might possibly be different : I can only say that I have never 

 been able to detect any such difference. , i j 



If indeed, the author's meaning be that these fringes extended 

 in any degree into the lateral fringes, it is obvious that they 

 would be mutually affected in a way conformable to previous ex- 

 One other remark of the author deserves especial attention*; 

 that, but for what he considers the incapacity for fuijher flexure 

 in the same direction, induced in a ray after one inflexion that 

 ray might be continually bent round an opake body ; and thus a 

 luminous object might be seen, though the whole of the body 

 intervened, or in other words, that we might see round a corner. 

 Now if such inflexion took place it would clearly be always 

 accompanied by a considerable diffusion of the light, so that 

 after a few successive inflexions it might be so much weakened 

 as to become imperceptible. . 



It is however a remarkable fact, that such an apparent in- 

 flexion does take place to a very great extent as I have pointed 

 out in a paper " On Luminous Rings round Shadows (Me- 

 moirs of the Royal Astronomical Society, vol. xvi. p. 306) and 

 which (as I have there mentioned) I believe to be a modifaca- 

 tion of the same phfenomenon, described rather obscure y by 

 Newton t and more distinctly by HookeJ, and apparently ac- 

 cordant with the theory of undulations (Ibid. p. 310). 



* Additional Observations, 4. 



t ?£'cu%us'p£Veets to have been .nuch overlooked, I shall 

 pei^haps be excused in annexing a bnef notiee of Dr. Hooke's experiment, 

 from a fragment on Light, appended to the Essay on Comets and Gra- 

 vity', in his ])osthumous works : London, 170&, P- lo^i- 



Ti-rht l)e ng admitted into a dark room through a very small hole and 

 received onascreenat some distance, on hohhng an opake body m the cone 

 of iTgh besides a " zone or fascia of light much brighter than the rest ot 

 the surface," along and outside the edge of the shadow which ^vas pro- 

 1 .bK [he first diftVaction fringe), be observed a faint liyht extending from 

 X. -4 intl^e S::; ; ancW'en the opake body was held so as to eovcr 

 nearly the whole of the luminous circk-, " rays were seen darting downwards 

 ^n^l,,UrXr lo the edge of the shadow, like the tail of a come, striking 

 'dZ^ldsviore than \i times, proiabUj 100 times their ''read l^r very 

 near lo u quadrant ," and growing fainter at greater distances. 1 he rays 

 were obviLsly occasioned by irregularities in the edge ; the rays were per- 



