RESULTS OF OBSERVATIONS OF COMETS VI. AND VII. 1 6 1 



determined with sufficient accuracy to permit the rigorous 

 calculation of the perturbations during the interval between 1844 

 and 1886. According to a communication by Dr. Krueger in the 

 Astronomisclie Nachrichten of April 15 last, the period of the 

 Comet VII., 1886, is 2,433 days, whereas that assigued to DeVico's 

 Comet by Brunnow is 1,994 days. It will thus be seen that 

 irrespective of the question of identity, the Comet VII. is an 

 exceedingly interesting one, in consequence of the shortness of its 

 period. It was observed at Windsor by means of the square bar- 

 micrometer on the Grubb 8 inch equatorial from October 8 to the 

 end of the year, but it was throughout a very faint and difficult 

 object. A table appended hereto contains the positions derived 

 from these observations. 



Reduction of the Star Places, &c. 

 In the determination of the mean places of the stars compared 

 with the two comets I have availed myself of every authority in 

 my Observatory library. In some few cases the comparison stars 

 could not be identified ; they will, therefore, have to be observed 

 in the meridian in order to render them available for determining 

 the comet places. I may here state that in working up the mean 

 place of Star No. 15 compared with Winnecke's Comet on 

 September 10, I found a considerable discrepancy between the 

 results derived from the Catalogues of Lalande and Lamont, the 

 only authorities available. I accordingly suspected a considerable 

 proper motion of this star. As there was no well-determined star 

 sufficiently near to it to be compared with it by means of the filar 

 micrometer of my large equatorial, I sought the assistance of Mr. 

 Lenehan, our Acting Government Astronomer, in determining its 

 accurate position. He accordingly very kindly observed it for me 

 with the 6 inch transit circle of the Sydney Observatory on the 

 evenings of July 27, 28, 29, 30, last. The apparent places thus 

 derived I have reduced by means of Peters' elements to the mean 

 equinox and equator of 1886 0. The following comparison of this 

 position with the positions derived by precession alone from the 

 Catalogues of Lalande and Lamont will at once show a very 

 considerable proper motion of this star in both co-ordinates. 



Authority and Epoch. Mean B.A. 1886-0. Mean N.P.D. 1886-0. 



h. m. s. o , „ 



Lalande, 1800 ... 14 25 1-06 ... 105 6 33-4 

 Lamont, 1850 ... 14 25 2-17 ... 105 6 56-6 

 Lenehan, 1887 ... 14 25 2-67 ... 105 7 14-2 

 In conclusion I may state that the reduction of the star places 

 and the calculation of the parallax factors have been effected in 

 duplicate by different forms. For the parallax factors j) and q 

 denote respectively the parallax corrections of the comet in seconds 

 of time and seconds of arc, and JPthe comet's equatorial horizontal 

 parallax in seconds of arc. 

 K— September 7, 1887. 



