Mifcellanea Curiofa. 9 9 



was diffufed into an oblong Form, was, by the 

 fecond, reduced into an orbicular one, with as much 

 regularity, as when it did not at all pafs through 

 them. So that whatever was the caufe of that 

 length, 'twas not any contingent Irregularity: 



1 then proceeded to examine more critically, 

 what might be effected by the difference of the 

 incidence of Rays coming from divers parts of 

 the Sun • and to that end, meafur'd the feveral 

 Lines and Angles belonging to the Image. Its 

 diftance from, the Hole or Prifm was twenty two 

 Foot; its utmoft length Inches; its breadth 

 2! ; the Diameter of the Hole \ of an Inch ; 

 the Angle, with the Rays, tending towards the 

 middle of the Image, made with thofe Lines, in 

 which they would have proceeded without Refra- 

 ction, was 44 0 5-6'. And the Vertical Angle of 

 the Prifm, 63 0 12 Alfb the Refractions on 

 both fides the Prifm, that is, of rhe Incident, and 

 Emergent Rays, were as near, as I could make 

 them, equal, and confequently about 54 0 4'. 

 And the Rays fell perpendicularly upon the Wall. 

 Now fubducting the Diameter of the Hole from 

 the length and breadth of the Ima^e, there re- 

 mains 1 3 Inches the length, and i\ the breadth, 

 comprehended by thole Rays, which palled thro' 

 the Center of the faid Hole, and conlequently 

 the Angle of the Hole, which that breadth fub- 

 tended, was about 31', anfwerable to the Sun's 

 Diameter ; but the Angle, which its length fub- 

 tended, was more than five fiich Diameters, name* 

 ly 2° 49/. 



Having made thele Obfervations, 1 firft com- 

 puted from them the refractive Power of that 

 Glafs, and found it meafur'd by the ratio of the 

 Sines, twenty to thirty one. And then, by that 

 mtioy I computed the Refractions of two Rays 

 H z flowing 



