“He calculated to within a month the return in 1759 of Halley's comet to its perihelion.”

“At perihelion, when proper motion reaches its maximum, it exceeds the diurnal motion, and the Sun turns slowly retrograde for a week.”

“There is a small periodic effect called nutation superimposed on precession caused by the motion of the perihelion of the Moon.”

“This tendency of the perihelia to crowd together in two opposite regions has been noticed by different writers.”

“The extremes of temperature at perihelia and aphelia to which comets are subjected did not bother him particularly.”

“At the second, Encke's comet and all others with perihelia within Mercury's orbit would have shared a similar fate.”