148 Astronomical Society. 



known are the Strombus Oniscus of Linna?ans ; a fossil species, 

 O. Cithara ; and two other recent ones, cancellata and tuber- 

 culosa. — The Lamarckian genus Pyramidella is modified so as 

 to include all the shells which accord in the following cha- 

 racters : " Shell turrited, smooth, very rarely slightly ribbed, 

 polished; volutions numerous, apex acute; aperture rather 

 oblong acute, above, rather rounded at the base ; outer lip 

 slightly expanded, turned upwards at the base and united to 

 the twisted columella; columella generally plaited." — The only 

 shells admitted by Mr. Sowerby into the genus Pyrida of La- 

 marck, are such as are commonly called Figs in commerce, 

 distinguished from all others by their thinness, and by the 

 regularity of their form. — From the Linnsean Mactrcc are se- 

 parated the Lutrarice and Anatince, the original generic ap- 

 pellation, however, being retained. 



XX. Proceedings of Learned Societies. 



ASTRONOMICAL SOCIETY OF LONDON. 



June 9. — r rHE reading of the Rev. Fearon Fallows' s paper, 

 ■*■ on the Small Transit Instrument, was concluded. 

 Mr. Fallows's directions maybe comprehended briefly in the fol- 

 lowing particulars : 1. Place the transit instrument as near the 

 meridian as possible, and also substantial meridian-marks at a 

 considerable distance both to the north and south. 2. The clock 

 must be set forward to sidereal time, and its daily rate obtained. 

 3. Observations of pairs of high and low Greenwich stars must 

 be made each evening along with others whose right ascensions 

 are required. 4. The apparent right ascensions of the Green- 

 wich stars must be computed up to the time of observation, or 

 taken from the Nautical Almanac. 5. The azimuthal error 

 must be found, if possible, by several of those pairs. Also, 6. 

 The error of the clock at the transit of one of the Greenwich 

 stars. 7. Reckon this error constant to every observation 

 made during the same night. 8. The azimuthal error must 

 be considered with a contrary algebraic sign for stars between 

 the zenith (of the Cape) and the pole. 9. A proportional part 

 of the daily rate must be applied to every observation from 

 the first. 10. The error of each star from the true meridian 

 must be computed from tables prepared for the purpose. 

 11. To the time of transit of each star, add the error of the 

 clock (6), the proportional part of the daily rate (9), and the 

 error from the meridian (10); the respective sums will give 

 the true apparent right ascensions required. 12. Compute 



the 



