294 A S T R O f? O M f.

Motion or Revolution of a Cdmet a ;$the Sun ; arid as this Sort of Mo 1 ' 10 ^:

PI. Lx.Fj g- 3-

that of the Earth;- whence those Cones are .j^tt lCFigures, and so have their Heights proportional .Diameters of the Bases. Therefore fay, As the jyjoO 11ter of the Earth 100 is to the Diameter of th e a to

doW slT t li«

28, so is the Altitude of the Earth’s Shthe Altitude of the Moon’s Shadow 60 ?-o& jyfoO 1 'Earth’s Semidkmeters.- The Shadow of the pis"therefore will just reach the Earth in her we 3 ^tance, which it cannot do in her Apogee ; hutPerigee it will involve a small Part of the Earth Sface.. , r e > 5

6. Besides the Dark Shadow of the Moon, * . tOanother called the Penumbra , or Partial Shau°p tl> erepresent which let S be the Sun, T the Earth,Moon ; and let K C F and ABE Se tWo Lin cS ,,ing the opposite Limbs of the Sun and Moon ; £ ‘ gh 3 'evident that C F E B will fee the dark or ab^ U g a stl**dow of the Moon, in which a Person on theSurface between' E and F is wholly deprived of tsl 0 th e 'Light. Moreover,- Let K B G and A C H beLines touching the Sides of the Sun and M °°rhately, and intersecting each other in the point uoV e 'the Moon. Then will HCBG be the Peniun^Q \ 0 jmentioned, and is the Frustum of the Con e jFfor ’tis evident that a Part of the Sun will b e t

Part thereof hid to a Spectator on the Earth s ^ f ro^:'between F and H, and E and G, or in otherthe Sun in those Parts of the Earth will apP epartially eclipsed. , ^ dP j

7. To calculate the Angle of the Cone H 1 ^Lesi 1 * 1SB, then in the oblique Triangle BIS, the e „<#Angle B I D is equal to both the inward andAngles IBS and I S B ; but I S B is that und^

theS^fP

the Semidiatneter of the Moon appears at t—is therefore insensibly small ; whence the Ang s t*r IB S or KBS = the apparent Semidiatn® QouSun. Therefore the Part of the Penusttb 1 q J