3 8 Mtjcellanea Curio] a. 



cpfofite to the Sun) the Colours of the his be 

 feen in the drop, then the Proportion fought 

 will be obtained with a little Calculation. It 

 is a Cubical Equation, explicable by one only 

 Root, by which, from the Primary Iris given, the 

 Ratio is computed, viz.. T 3 ~-*3 T z t — 4rrt=o, 

 where T is the Tangent of the Angle of Inci- 

 dence requifite, t the Tangent of $ the diftance 

 of the Iris from the Point oppofite to the Sun, 

 to the Radius Whence (according to 



Cardanw** Rules) arifes this Theorem, viz.. 

 From the Cube of t fubftratt the Product of 2tr 

 into the Excefs of the Secant of the fame Arch 

 above the Radius ; the difference fhall be the leffer 

 Cube. The Sum of the fame , adding 4trr, will 

 be the greater Cube, The Sum of the fides of both 

 Cubes , and of t, will be equal to the Tangent of 

 the Angle of Incidence, and the half of that, will 

 be the Tangent of the RefraEled Angle, From 

 whence the Ratio fought is manifeft. 



Bor an Example of this. In a di 4 op of Oil of 

 Turpentine, the diftance of the Primary Iris, 

 from the Point oppofite to the Sun, is ob- 

 ferved to be 25 0 . 40'. ? Tis required to find 

 the Ratio of the Refradion. 



t-Tang. 12°. 50'. =2 0,2278063 



s~Sec. of the fame. ~ 1,0256197 

 ttt Be 0,01182217 



s— r*2tr == 0,0116 7255 



The Difference is the leffer Cube o, 000 14952 

 whofe fide o, 0530773 



The Sum o, 02349482 

 4trr 0,91122525 



Create^ 



