Part I:
Transit
March, 1759
Dr. Halley observed . . . how much greater irregularities must not a comet be liable to, which at its remotest distance gets near four times farther from the Sun than Saturn, and whose velocity in drawing near the sun needs but a very small increase to change its elliptic into a parabolic curve.
—Charles Messier,
A Memoir, containing the History of the Return of the famous Comet of 1682, Phil. Trans., Jan. 1765