Of Light and Colours.

Sir Isaac Newton found, by a very curiousand convincing Experiment, that the Rays

of

(CXlJf) i. Let f) E KI be a double Convex Lens,N its Centre, and N D the Radius of Convexity at D ;E V its Axis, and H E a Beam of the Sun’s Light inci-dent on the Lens parallel to its Axis in the Point F.Let AB C be a Prism touching the Lens in the PointsE and D, and it is evident the Law and Manner of Re-fraction of the Beam at E will be the fame, whetherWe consider it as made through the solid Glass PrismABC, or through the Lens DEK, because the Pointof Incidence E is the fame in or common to them both.

2. The Beam being refracted at D, it is plain theRefraction will be there also made into the Air in thefame Manner from the Lens as from the Priftn, suppos-ing them to touch in the Point D. Let ND be con-tinued to L, then will L D be perpendicular to theLens in D ; and the Refraction being made into theAir, (a rarer Medium) the refracted Rays will tend to-Wards the Axis, and meet it sooner or later as they areMore br less refrangible. Thus the most refrangibleRays D W will cut the Axis in G, the least refrangibleRays D T in Qj, and the mean refrangible Rays in O ;2nd the others in the intermediate Space between O and.G, and O and G- The fame is to be understood ofthe Beam I K on the other Side the Axis;

3: Hence we fee, that in the Axis of the Lens theImages Of an Object will be formed in several PartsLom G to Qj by which means the Object will appearRed at G, Violet-colour d. at Q_* and of other Hues irtthe Parts between. Nor are we to understand thatRven Images only are formed by the seven Sorts ofRays ; but each particular Sort of Ray, according tothe Intensity of the Colour^ from the strongest to theLintest Part, consists of an indefinite Number of dift'e-Wntly refrangible Rays, each of which will form anynage'of the Object in its proper Focus ; And there--st r e we may conceive as- many Images formed in the“Pace from G to Qp as there are Points in the Line G Q.

Y 2 4. The

3 2 3

PlateXXXVII-Fig. 4 -