d|Least Dist.| Gr. Dist. |
| | Passage. | Passage obs. | Years.|Ast. Units.|Ast. Units.|
+------------+-----------------+-----------------+-------+-----------+-----------+
|Halley | 1456 June 8.2 | 1835 Nov. 15.9 | 75.9 | 0.58 | 35.42 |
|Biela | 1772 Feb. 16.7 | 1852 Sept. 23.4 | 6.67 | 0.98 | 6.18 |
|Encke | 1786 Jan. 30.9 | 1905 Jan. 11.4 | 3.29 | 0.34 | 4.08 |
|Tuttle | 1790 Jan. 30.9 | 1899 May 4.5 | 13.78 | 1.03 | 10.53 |
|Poris | 1812 Sept. 15.3 | 1884 Jan. 25.7 | 72.28 | 0.78 | 33.70 |
|Olbers | 1815 April 26.0 | 1887 Oct. 8.5 | 73.32 | 1.21 | 33.99 |
|Winnecke | 1819 July 18.9 | 1898 Mar. 20.4 | 5.67 | 0.77 | 5.55 |
|Faye | 1843 Oct. 17.1 | 1896 Mar. 19.3 | 7.50 | 1.69 | 5.93 |
|De Vico | 1844 Sept. 2.5 | 1894 Oct. 12.2 | 5.66 | 1.19 | 5.01 |
|Brorsen | 1846 Feb. 11.1 | 1879 Mar. 30.5 | 5.52 | 0.65 | 5.63 |
|D'Arrest | 1851 July 8.7 | 1897 May 21.7 | 6.56 | 1.17 | 5.71 |
|Tempel I. | 1867 May 23.9 | 1879 May 7.0 | 5.84 | 1.56 | 4.82 |
|Tempel-Swift| 1869 Nov. 18.8 | 1891 Nov. 15.0 | 5.51 | 1.06 | 5.16 |
|Tempel II. | 1873 June 25.2 | 1904 Nov. 10.5 | 5.28 | 1.34 | 4.66 |
|Wolf | 1884 Nov. 17.8 | 1898 July 4.6 | 6.80 | 1.59 | 5.57 |
|Finlay | 1886 Nov. 22.4 | 1893 July 12.2 | 6.64 | 0.99 | 6.17 |
|Brooks | 1889 Sept. 30.3 | 1903 Dec. 6.5 | 7.10 | 1.95 | 5.44 |
|Holmes | 1892 June 13.2 | 1899 April 28.1 | 6.89 | 2.14 | 4.50 |
+------------+-----------------+-----------------+-------+-----------+-----------+

There are also a number of cases in which a comet has been observed
through one apparition, and found to be apparently periodic, but which
was not seen to return at the end of its supposed period. In some of
these cases it seems likely that the comet passed near the planet
Jupiter and thus had its orbit entirely changed. It is possible that in
other cases the apparent periodicity is due to the unavoidable errors of
observation to which, owing to their diffused outline, the nuclei of
comets are liable. (S. N.)

COMET-SEEKER, a small telescope (q.v.) adapted especially to searching
for comets: commonly of short focal length and large aper