i oc Mifcellanea Curiofa. 



flowing from oppofite parts of the Sun's d*fcut 9 

 io as to differ 31' in their obliquity of Incidence, 

 and found that the emergent Rays fhould have 

 comprehended an Angle of about 31', as they 

 did, before they were incident. 



But becaufe this Computation was founded on 

 the Hypothecs of the proportionality of the Sines 

 of Incidence and Refraction, which, tho' by my 

 own Experience I could not imagine to be fo er- 

 roneous as to make that Angle but 31', which 

 in reality was ^ 0 49' ; yet my Curiofity caus'd 

 me again to take my Prifm. And having plac'd 

 it at my Window, as^before, I obferv'd, that by 

 turning it a little about its Axis to and fro, fo as 

 to vary its obliquity to the light, more than ah 

 Angle of four or five Degrees , the Colours were 

 not thereby fenfibly tranflated from their place 

 on the Wall, and confequently by that Variati- 

 on of Incidence, the quantity of Refraction was 

 not fenfibly varied. By this Experiment there- 

 fore, as well as by the former Computation, it 

 was evident, that the difference of the Incidence 

 of Rays, flowing from divers parts of the Sun 

 could not make them, after decuffation, diverge 

 at a fenfiblygreater Angle, than that at which they 

 before converged ; which being, at moft, but 

 about thirty one or thirty two Minutes, there 

 frill remain'd fome other caufe to be found our, 

 from whence it could be two Deg. 49 Min. 



Then I began to fufpe£i, whether the Rays, 

 after their TrajedYion through the Prifm, did 

 not move in curve Lines, and according to their 

 more or lefs Curvity, tend to divers parts of the 

 Wall. And it increas'd my fufpicion, when I 

 reniember'd that I had often feen a Tennis-Ball, 

 ft ruck with an oblique Racket, defcribe fuch a 

 curve Line. For a Circular as well as a Pro- 



greffive 



