On the AffeBUns af Ligtit.— Colour.t from specula, ipj 



fight. In like manner, thofe formed by a double flexion of two bodies, and thofe made out 

 of homogeneal light, were feen to a much greater number when carefully vkwed througk 

 the prifm. And this experiment I alfo tried with all the fpecics of fringes by flexion which I 

 could think of. 



Obfervation 9. The fame appearances which were occafioned by the metal fpeculum, 

 might be naturally expeflcd to appear when a glafs one was ufed. But I alfo found the like 

 rings or fringes of colours and fpots in the image beyond the focus of a lens ; nor was a very 

 excellent one belonging to a Dollond's telefcope free from them, 'i'he ringB with their darfc 

 intervals refembled thofe floating fpecics fo often obferved on the furface of the eye, and call- 

 ed " mufcae volitantes," only that the mufcae are tranfparent in the middle, becaufe formed 

 by drops of humor: they will, however, be found to be compaflTed by rings of faint colours, 

 which will become exceedingly vivid if the eyes be fhut and flowly opened in the fun's tight, 

 fo that the humor may be coilefled ; they alfo appear by reflexion, mixed with the colour* 

 defcribedin Phil. Tranf. for 1796, p. 268, (or Philof. Journal I. 593) 



Obfervation 10. The fun (hining ftrongly on the concave metal fpeculum, pliiced at fucH 

 adillance from the hole in the window that it was wholly covered with the light ; upon in- 

 clining it a little, the image on the chart was bordered on the infide with three fringes 

 iimilar to thofe already defcribed : on increafing the inclination thefe were- diftended, be ■ 

 coming very bright and beautiful : when the inclination was great, and when it was ftill in-j 

 creafed, another fct of colours emerged from the fide next the fpeculum, and was concive 

 to that fide. Her» I {lopped the motion, and the image on both fides the focus had three 

 fets of fringes, and four fringes in each fet ; but when viewed through a prifm (as before 

 defcribed), the numbers greatly increafed, both the fringes and the dark intervals decreafmj 

 regularly. The appearance to the naked eye is reprefented in fig. 6, plate VII. where ADO 

 being the image, A and C are the fets of fringes at the edges, and li the third fet, there 

 being none at E and D the fides, fince the light which illuminates thefe quarters comes not 

 from the edges of the fpeculum in fo great inclinations. I now viewed the furface of the 

 fpeculum, and faw it in the place anfwering to B in the image, covered with fringes exa6ily- 

 correfponding with thofe at B } and on changing the figure of that part of the fpeculum's 

 edge between them and the fun, the fringes likewife had their figure altered in the very fame 

 way. On moving the fpeculum farther round, B came nearer to A in the image, according 

 as the fringes on the fpeculum receded from that fide which formed them; and before they 

 vaniflied alike from the fpeculum and image, they mixed with the colours at A in the image^- 

 and formed in their motion a variety of new and beautiful compound colours ; among thefe I 

 particularly remarked a brown chocolate colour, and various other (hades and tinges of brown 

 arid purple, Juft before the fringes at B appeared, the fpace between A and C was filled 

 with colours by reflexion, totally different in appearance from the fringes ; but I could not 

 examine them f&minutely as I wilhed in this broad image. I therefore made the following 

 experiment : 



Obfervation 11. At the hole in the window-fliut I held the fpeculum, and, moved rt.toi 

 fuch an inclination that tke colours by reflexion might be formed in the image: they were 

 much brighter and far more diftended than the fringes, and were in every rcfpei^ like 

 the images by reflexion in the common way, only that the colours were a little better and 

 more regular. They were alfo feen on the fpeculum, as the third fat of fringes had before 



C c 2 been 



