72 Royal Astronomical Society. 



rential coefficients of the fourth order, and some small additional 



aberration terms. These approximations are so conducted, that the 



quantities obtained are corrections to the first obtained values, and it 



is consequently not necessary to calculate with seven-figure logarithms. 



j? dv dz 

 The values of X2, ya, z-i, — -, — , — -, beinjr thus obtained as ac- 

 y dt dt dt & 



curately as possible, the elements of the orbit are readily derived by 

 known formulae. As the observed right ascension and north polar 

 distance were not corrected into latitudes and longitudes, the ele- 

 ments are by tins calculation referred to a plane through the sun's 

 centre parallel to the earth's equator in a given position. By a 

 simple computation they may be transferred to the plane of the eclip- 

 tic. But the original form is the most convenient for obtaining 

 geocentric co-ordinates in terms of the eccentric anomaly, for the 

 purpose of calculating an ephetneris, and also for deriving equations 

 of condition by which the elements may be corrected by future ob- 

 servations. The method of doing this the author proposes to describe 

 at another opportunity. 



A brief Notice of the Imperial Observatory of Poulkova. By the 

 Astronomer Royal*. 



The observatory of Poulkova was built on the plans furnished by 

 its director, M. Struve ; the instruments are, for the most part, 

 constructed according to his special instructions. The peculiar 

 scope of this noble establishment is sidereal astronomy in its widest 

 sense ; and Mr. Airy strongly expresses his admiration of the defi- 

 niteness of the purpose which M. Struve had in his mind, and of the 

 thorough manner in which it has been carried into effect. He says 

 that " no astronomer can feel himself perfectly acquainted with mo- 

 dern astronomy in its most highly cultivated form, whether as regards 

 the personal establishment, the preparation of the buildings, the 

 selection or construction of the instruments, or the delicacy of using 

 them, who has not well-studied the observatory of Poulkova. To 

 this excellence many antecedent circumstances have materially con- 

 tributed. The first of these is the personal character of M. Struve ; 

 his mature experience obtained before the intention of building the 

 new observatory had been formed ; his vigour in arranging the plans 

 on a large scale, and in superintending constructions even to the 

 minutest point, and his perseverance and skill in arranging the sub- 

 sequent proceedings of the observatory." The liberality of the 

 emperor, the freedom of choice as to site, instruments, &c, have been 

 admirably employed by the director. The character of the buildings, 

 in addition to their perfect suitability to their design, is that of splen- 

 dour without extravagance. The foundations are most carefully 

 laid, and solid beyond any former example \. 



The large equatoreal, by Merz and Mahler, is the instrument which 

 has principally extended the fame of the Poulkova Observatory. 



* The Astronomer Royal visited Poulkova last summer, and gave orally 

 as account of the Observatory at the meeting of the Society in November, 

 the substance of which was communicated in a letter to Professor Schu- 

 macher, and printed in the Aslronomischc Nachriehten. 



f The Observatory and its instruments may be well understood from the 



