48

O P T I C Si

lower Eye-Glass D E; and this Image !§viewed by the Eye through the upper Eye' 1

Glass

will e E be the Axis of the Pencil of Rays proceediflSfrom the Point eto the Lens D F, of which e F beislSone, it will be refracted into F I parallel to e E ; a* 1 ®so the Angle F I E = C E e. But F I E is the Ang^under which the Image is viewed through the Les' 5D F, which is to the Angle C O A as CO to CTherefore the third and last Part of the Ratio for mag"

... • CO

mfyingis

19. If now we compound the several Parts of the Ra'tio now found into one, it will make the Ratio 0

g-g- X X — to 1. For Example, let e c = § al*

Inch, fH = 3I-, er — 2, CE= if ; then HE being2, and HO — 11,66, we have CO — 10,66 ; when cS

the above Ratio in Numbers will be ——X

L5 3>5

—— — 4.0,87. Therefore the Diameter of any Obje$?’ 5 .

is magnified near 41 times by such a Compound M 1erofcope.

20. If this Calculation be enquired into, we shall fib®that the Glass G K diminishes the magnifying PoWePwhich is greater by the Eye-Glass D F alone, and motfdistinct. Thus in Fig. II. of the large Plate XLVI*the lower Glass D E were taken away, the Rays wouygo on and be united in a Focus at the Points M, P, Tvand there form an Image of the Length MN; but bfreplacing the Glass D E we shall have the large Im^ 4 eM N contracted into a lesser m n. Now this larg^Image M N may be considered as formed by the L f ’b sD E at a negative Focus from an Object m n, wl>0qDistance F B is less than the focal Distance of theLens : All which is easy to understand from the for 6 "going Theory of Dioptrics .