Page 250 - 89 history of astronomy_opt
P. 250
described by the line from the planet to the
sun in equal times) was only another way of
saying that the centripetal force on a planet
is always directed to the sun. Also that Ke-
pler’s first law (elliptic orbits with the sun
in one focus) was only another way of say-
ing that the force urging a planet to the
sun varies inversely as the square of the dis-
tance. Also (if these two be granted) it fol-
250
