The extremes of temperature at perihelia and aphelia to which comets are subjected did not bother him particularly.
This tendency of the perihelia to crowd together in two opposite regions has been noticed by different writers.
The maximum occurs between 30 and 60, where thirty-five perihelia are found in 30 of longitude.
It is a remarkable fact, however, that the longitudes of their perihelia differ by almost exactly 180.
At the second, Encke's comet and all others with perihelia within Mercury's orbit would have shared a similar fate.
The point at which an orbiting object, such as a planet or a comet, is closest to the Sun. Compare aphelion, perigee.