130

Piate XVI.Fig. i.

Fig. 2.

Of Optics .

by the glass, as, that aster going out of it, they will become paralie!,as fhewn in the space cba.

15 the candle be placed nearer the glass than its focal distance, therays will converge aster paffing through the glass, more or less, as thecandle is more or less distant from the focus.

If the candle be placed farther from the glass than its focal distance,the rays will converge aster pafling through the glass, and meet ina point, which will be more or less distant from the glass, as thecandle is nearer to, or farther from its focus: and where the raysmeet, they will form an inverted image of the flame of the candle;which may be feen on a paper placed in the meeting of therays.

Hence, if any object ABC be placed beyond the focus F ofthe convex glass des, forne of the rays which flow from every pointof the object, on the side next the glass, will fall upon it, and asterpafling through it, they will be converged into as many points on theopposite side of the glass, where the image of every point will beformed : and consequently, the image of the whole object, whichwill be inverted. Thus, the rays Ad, Ae, Af flowing from thepoint A, will converge in the space das and by meeting at a, willthere form the image of the point A. The rays Bd, Be, Bf flowingfrom the point B, will be United at b by the refraction of the glass,and will there form the image of the point B. And the rays Cd,Ce, Cf, flowing from the point C, will be united at c, where theywill form the image of the point C. And so of all the other in-termediate points between A and C. The rays which flow fromevery particular point of the object, and are united again by theglass, are called fencils of rays.

If the object ABC be brought nearer to the glass, the picture abcwill be removed to a greater distance. For then, more rays flqwingfrom every single point, will fall more diverging upon the glass; andtherefore cannot be fo soon collected into the corresponding points behindit. Consequently, if the distance of the object ABC be equal to thedistance eB of the focus of the glass, the rays of each pencil will befo refracted by pafling through the glass, that they will go out of itparallel to each other j as di, eH,fh, from the point C-, dG, e K,fD,from the point B-, and d K, e E, fL, from the points: andtherefore, there will be no picture formed behind the glass.

If the focal distance of the glass, and the distance of the objectfrom the glass, be known, the distance of the picture from the glassmay be found by this rule, viz. multiply the distance of the focus

by