Of Light and Colours.

the Bottom of all Vessels, if covered withWater, appear raised, or higher by a fourthPart of the Depth of the Wate/, than whatthey really are (CXVII),

The

(CXVII) I. If Bodies, on which Light falls, weresupposed to affect it no other Ways than by giving Ad'mission to the Rays, or permitting them to pass throughtheir Substance, they would then persevere in the sain®Right Line after their Immersion, as before; andCourse' there could be no such thing as the Refractionabove defined. But Bodies are not passive to the Ray sof Light, but act upon them with a real and determi'nate Force, as is evidently proved by Experiments.Thus if a very small rpund Hole be made in a thinPiece of Metal, and the Light of the Sun transmittedthrough it into a dark Room ; if the Metal acted no con the Ray passing through the Hole, the Spot of L>g^

' would always be of the fame Size with the Hole at ahDistances from it; but because we always observe th 6luminous Spot is larger than the Hole, and the m° reso as it is farther distant, is a plain Proof that the Pp r 'rides of the Metal in the Periphery of the Hole act withan attracting Force on the Rays of Light, and infl e pthem in such a Manner as to cause them to proceed d>*verging from each other,

2. In like manner, if the Rays of Light are madepass between the parallel Edges of two Knives placeat the Distance of T ‘o of an Inch, we shall observe 0,1each Side the transmitted Beam a Glare of Light 1*^that of the Tail of a Comet, if the Beam be recei veon a Sheet of Pap:r, at the Distance of about j ° r jFoot from the Knives. And if the Knives are pwith their Edges about T Lo of an Inch apart, instead ®the Light above-mentioned, you’ll observe on each pithe Beam of Light, three Fringes of colour’d Lig* 1parallel to the Edges of the Knives, which aredistinct as the Hole of the Window or Beam of Lig>is less. rf

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