398 Royal Astronomical Society. 



circumstance may render the latter part of the series especially valu- 

 able, the southern position of the comet and the unfavourable state 

 of the weather causing the observations of it to be in general very 

 scarce, after its perihelion passage. 



II. Note on the Masses of Venus and Mercury. By R. W. Roth- 

 man, Esq. The following is the conclusion of this note, the whole 

 of which is given in the Society's Monthly Notices for January. 



On the whole, it is very remarkable that the planetary masses 

 given in the Me'canique Celeste (vol. iii. p. 61), satisfy the secular 

 motions affecting the orbit of Venus much better than the masses of 

 later astronomers. It appears that in later times the mass of Mer- 

 cury has been too much increased, and that of Venus too much di- 

 minished. What has been previously remarked concerning the 

 masses of Venus and Mercury is confirmed by the motion of the 

 node of Mercury. If this motion be calculated by theory with the 

 masses of the Mecanique Celeste, the result agrees almost exactly 

 with the motion determined from observation by Lindenau. — See his 

 Tabula Mercurii, p. 9. 



III. Observations of the Immersion of p 1 Leonis behind the Dark 

 Limb of the Moon. By R. Snow, Esq. 



The observed Ashurst sidereal time of the immersion was 15 h 

 37 m 23 s * 9. The observation was made with a power of 75 on the 

 telescope of the five-feet equatoreal, under very favourable circum- 

 stances. 



IV. Extract of a letter from Professor Encke to Mr. Airy, dated 

 20th December, 1841. Translated from the German. Communicated 

 by G. B. Airy, Esq. This communication will be found, entire, in 

 the preceding volume, p. 137. 



V. Comparisons of the Planet Venus in Right Ascension and 

 N. P. D. with the Star A. S. C. 423, made with the Equatoreal In- 

 strument of the Observatory at Ashurst, on April 9, 1841. By R. 

 Snow, Esq. 



The equatoreal instrument employed for these observations is of 

 Fraunhofer's construction, and furnished with clockwork ; the ob- 

 ject-glass is of five feet focal length, and of four inches aperture. It 

 is supported on a Very firm pier, and retains its position very well. 



The observations were made with a position micrometer, adjusted 

 for transit and declination observations. They consist of thirty 

 transits of the star and of the first limb of Venus over the meridian 

 wire, and of nine micrometrical measures of the differences of 

 N. P. D. of the star and the south limb of the planet : the corrected 

 sidereal times of the observations are given. 



The value of a revolution of the micrometer-screw had been de- 

 termined by 400 transits of stars near the equator. Measures of the 

 semidiameter of Venus were made at the same time, by which it 

 was found that the measured value exceeded the tabular value given 

 in the Nautical Almanac by 8**1. 



The circumstances of the observations were favourable. 



VI. Reduction of Mr. Snow's Observations of Venus and the Star 

 A. S. C. 423, with some remarks upon the employment of equa- 



