smites, at the2 40,000 Miles.

STRONOMY.

117

mean Distance of about

fi

^idc;

Jupiter

*.L ,

eir Sides next the Sun, and their oppositethem t er 3sb r ’ght circular, which infallibly provesl h ere 0 ° e deep, hollow, round Cavities ; of whichUpp er p e two very remarkable ones near together on thethe fyj art , a nd may be viewed exceeding plain when9, is about four or five Days old.

CUr iou s p mea ^ ure the Height of a Lunar Mountain is aM ; n S Fr °blem, and at the fame time very easy to ef-^" eri tr e p following Manner. Let C be the Moon’sSurf ace ’, bB a Ray of the Sun touching the Moon’s^B ar J nF b anc ^ the Top of a Mountain in B. Drawf 0lJ , ^ ^ > the Height of the Mountain A B is tot^hat p ’ With a Micrometer in a Telescope findtain B ^portion the Distance of the Top of the Moun-ts H; a r ° m the Circle of Illumination at D, bears tothe Li n rtl< llf r of the Moon, that is, the Proportion ofMil es t DB to DF; and because D F is known in

to.’hr

of pj 0V/ a ^tnit that D B : D C :: 1:8, as in one

^ 6 5 =

Lre b

^eighr C T~ AC = 8,062 —'8 = 0,062 — AB, the

\ ,q**L r\<. , 1 _ __ *

.D B will be also known in that Measure,admit that D B : D C :: 1:8,it will be ; then D C* -f- D B 1 = 64 -f- 1B 1 whence \/65— 8,062 — B C; where-

•iiHf r , — — v/, yuA ^ ’ 7 .

A B 8 f the Mountain required. Wherefore A C :

' 0,062 :: 8opo : 62. And since the Moon’sA Id 96 ^ 0 — 1096 Miles, therefore 8000 : 62"hies jji ’^’5 nearly. This Mountain then being 8|’ ' s nearly three times higher than the highest

I, ^"Tn the Earth. _

9 top, j .8am, the Cavities are proportionably large andio 0 J t L V l°^f erve d Cavities in the Moon more thanHie}, . h Part of the Moon’s Diameter in Breadth,jjstir De Joout 200 Miles upon the Moon’s Surface;V av 'ties th S a PF iear hkewife proportional. The Lunar^’autain 6le ^ ore P ro <-hgiously exceed the Height of thes > and consequently the Surface of the MoonI o has

PI. LIT,Fi g- 5 -

4