LET. XVIII. OF THE SUN, MOON, AND PLANETS. 305

the earth on its axis, in the fame time thatVenus moves from F to f in her orbit. Then,when Venus is at F, she will appear on the funat K, as seen from the earth’s center, whilst tothe observer at a, fire will not yet be cometo the sun, but if she were then visible, wouldbe seen in the line a F H towards the east,and must move on from F to G in her orbit, be-fore the observer would see her on the sun at K,in the right line a G K. So that her transit willbegin as much later to the observer at a, than itdoes to the observer at C, as sire is in movingfrom F to G, in her orbit.

When Venus comes to g in her orbit, the ob-server will be carried from a to b, by the earth’smotion, and then he will fee her in the line bgL, just beginning to leave the fun at L; butflie must move on from g to f in her orbit, be-fore she begins to leave the fun at L, as seen fromthe earth’s center C, in the right line C fL ;and then, to the observer at b, she will appearquite clear of the fun to the west, in the line8/1. So that the whole duration of the transit,from K to L on the fun, will be shorter as seenby the observer in motion, from a to />, than asseen by the supposed observer at rest at theearth’s center C. For to the former she willwove only from G to g in her orbit, during thetime she appears to move from K to L on thefun: but to the latter, she must move from

X F to