*

d

88

Appendix II.

distinctcr by the two Glasses H I and XJ 8together, than it would do by the singl eEye-Glais M N alone, in Proportion asT P is greater than T Qj all which is evi-dent from the foregoing Principles of Optics-

W i t H respect to the Lens A E D, if ^be a small one, and the focal DistanceC F be short, then will it represent th eObject-Glass of a Microscope, and the smallObject O B will be viewed to much greatsAdvantage by Means of the two Ey e "Glasses H I and US, than by a single Ey e "Glass alone M N. Whence the Reason I sevident of the usual Construction of th* 5Instrument, as we have before shewn.

But if AE.DG be the Object-Glassa Telescope, and FC its Focus, then vviHO B represent a distant Object, vvh 0 ^Image W L is that which is viewed by asingle Eye-Glass M N in what is called' Astronomical ‘Telescope ; but this Imagemore distinctly viewed by two Glasses I astT, than by one alone; and therefore f uC ^a Telescope should consist at least of th reeGlasses.

In the common Telescope the Imag eL W is considered as an Object, and anO'ther Image is formed of it, as was shetvnFigure 8, of Plate XLVIII, and as ^

m

have now shewn that each Image req

uires

the