ON THE ORBIT-ELEMENTS OF COMET L, 1880. 41 
1849,” viz. 20,923,700 English feet or 3,962'822 English 
miles. It appears now that towards the close of January the 
comet was rapidly approaching the sun from the regi ing 
south of the ecliptic. It proceeded, of course, with accelerated 
velocity towards that luminary, and at thirty-six minutes past 11 
o'clock on the morning of the 27th (Sydney mean time) or just 
twenty-four hours before perihelion, it arrived at a point 9,584,500 
miles from the sun’s centre. At twenty-seven minutes 1 
o’clock a.m. on the 28th it crossed the plane of the earth’s orbit at 
a distance of 1,074,600 miles from the same point. Its course 
now lay on the north side of the ecliptic, and sixty-nine minutes 
later it arrived in perihelion or that point of its orbit nearest to 
thesun. The distance between the sun’s centre and the centre of 
gravity of the comet at this moment according to my elements was 
621,380 miles. The semi-diameter of the sun at the earth’s mean 
- distance, resulting from twelve years’ observations, 1836 to 1847, 
at the Royal Observatory, Greenwich, is 16'1’°82. If we adopt 
this value and execute the necessary calculation we shall find that 
at the instant of perihelion passage the comet’s centre was actually 
only 190,480 miles distant from the sun’s. surface. The heat to 
which the comet was subjected at this point of its path in space 
must have been something beyond human conception, and the solar 
orb itself subtended an angle of 88°, or 165 times greater than its 
apparent diameter as seen from the earth. Sir John Herschel says 
that “the comet of 1680, whose perihelion distance was 0-0062, and 
which therefore approached the sun’s surface within one-third part 
of his radius (more than double the distance of the comet of 1843) 
was computed by Newton to have been subjected to an intensity 
of heat two thousand times that of ot iron,—a term of com- 
ison indeed of a very vague description, and which modern 
thermotics do not recognize as affording a legitimate measure of 
radiant heat.” After leaving perihelion the angular velocity of our 
i om the sun 
rapidly increased. At twenty-seven minutes past 1 o’clock in the 
afternoon of the 28th the comet from the north tothe south 
side of the ecliptic, at a distance of 1,473,300 miles from the sun’s 
centre. It thus appears that the comet was only three hours on 
the north side of the plane of the earth’s orbit, and in this brief 
Space of time it of course described an arc of 180°, or just one-half 
of its apparent path in the heavens as seen from the sun. I find 
by a rough calculation that if the perihelion passage had occurred 
comet across the sun’s 
during the interval I have described, was pursuing its path unseen 
from our planet, and it was not till the Ist day of February that 
its huge tail was detected from several parts of the southern 
