3io Of Light and Colours.

Sun X Y, which is, perhaps, one of themost surprizing and agreeable Spectacles of.Nature.

THE

taken from the Q_D K or QJ 3 D (— 32° = half theAngle of the Prism) gives the Angle K D I or L D S— 31 0 59' 26", and so the Sine of the Angle of Inchdence in Vacuo (32 0 ) is to the Sine of the Angle ofRefraction into Air (31° 59^ 26") as 1000000 to999736. (See Mr. HawkJbee s own Figures in Platf.35. Fig. 7, 8, 9.)

29. In order to understand the Difference between thetrue and apparent Places of Objects, seen through aMedium of different Density from the Air, let theScheme be constructed as in the Figure, where the Sines

Plate of Incidence and Refraction are H L and G I; andXXXIV. these are in a given Ratio of A to B, that is, H L •Pig. 9. G I :: A : B ; but because of parallel Lines N Q_K Cwe have HL = NK; therefore NK:IG::A:BuNC : IC=HC ; but N C : H C :: C E : C M, be-cause P E is parallel to K D, therefore C E : CMrA : B.

30. Now since the Ray E C coming from an Objectat E is refracted in the Air into the Ray HC ; if H Cbe continued to F, the apparent Place of the Objectwill be in the refracted Ray at M in the PerpendicularE P, and projected to F on the horizontal Plane O P*.but the Point M will always be the visible Place of th eImage ; therefore when the Angle C E O is indefinitelysmall, or the Point C coincides with O, the Lines Cband C M will become O E and O M ; and in that cd e rOE : OM :: A : B ::p 3, in Water. Whence ’t>®evident that the apparent Place of an Object immersedjn Water, and view’d in the Perpendicular, will be

3 of the Depth of Water.

31. But if the Medium be Glass, then O E : O

3 : 2, or more nearly as 17 to u ; so that Jj-O EO M, or the apparent Place of an Object seen through

a Medium of Glass, will be at the Distance of i 7 °-

the