PHYSICAL AND LITERARY. 35 



4s- ftill more extraordinary than in the 

 former: infomuch that the hole feen thro' the 

 prifm appears uniformly of this yellow, and as 

 <iiftind:ly terminated as thro' a plain glafs ; ex- 

 cept that there is adjoining to it on the upper 

 ^de a very faint ftream of green and blue. 

 White bodies illuminated with it, appear alfo 

 thro' the prifm perfedly well defined ; both 

 which are very furprizing phcenomena to thofe 

 who have been accuftomed to the ufe of the 

 prifm in other heterogeneous lights, where it 

 never fails to throw confufion on the extre- 

 mities of all vifible objeds. 



29. Because the hole appears thro' the 

 prifm quite circular and uniform in colour j 

 the bright yellow which prevails fo much 

 over the other colours, muft be of one de- 

 termined degree of refrangibility ; and the 

 tranfition from it to the fainter colour ad- 

 joining, not gradual, but immediate. 



30. Upon examining foap-v/ater-films in 

 the fame light, I could only obferve lumi- 

 nous bands feparated by dark ones ; the green 

 and blue being too weak to afted; my eye in 

 this view. Jt would be needlefs labour to 

 enter here into a particular detail of the rea- 

 fons of the different transformations of co- 

 loured 



