ASTRONOMY. 381 



Of the 4051 stars particularized in the catalogue, there are 349 whose 

 spectrum could not be surely made out. The remainder are divided 

 among Vogel's classes as follows; Class la, 2155, Class 16, 10, Class 

 II«, 1240, Class Illfl, 288, Class Illb, 9 stars. 



Among the brighter stars with very beautifully distinct spectra that 

 therefore can be seen with weaker powers may be mentioned — 



In Class Ifl. y Geminorum, a Leonis, ft Leonis, a Ophiuchi, a Aquila?, 

 a Pegasi. 



In Class Ila. a Tauri, a Bootis, a Serpentis, ft Ophiuchi, a Ophiuchi, 

 y Aquilae, e Pegasi. 



In Class Illfl. a Ceti, a Orionis, 5 Virginis, a Herculis.— (The Observ- 

 atory, November, 1883.) 



Photometry of stars. — At the meeting of the Royal Astronomical So- 

 ciety, May 11, 1883, Prof. C. Pritchard, of Oxford, gave an account of 

 his recent expedition to Cairo, and of the work on which he has for the 

 last two years been engaged, viz, the measurement of the magnitude 

 of the stars visible to the naked eye from the pole to the equator, in- 

 cluding at present all those brighter than the fifth magnitude. This 

 work is now complete. He found that at Oxford, Laplace's law of altera- 

 tion of a star's light as measured in magnitude — according to the secant 

 of the star's zenith distance — did not hold good for zenith distances ex- 

 ceeding 05°, and that for stars at lower altitudes the alterations in ap- 

 parent magnitude were conflicting and not satisfactory. For the pur- 

 pose of accurately investigating the effect of atmospheric extinction of 

 light under better circumstances, he chose the climate of Upper Egypt, 

 where the atmosphere is uniform and stable, as the proper locality for 

 repeating the Oxford observations, and rendering the research com- 

 plete. A duplicate set of instruments was left at Oxford in charge of 

 the senior assistant, who observed the same stars with Professor Prit- 

 chard at Cairo. The results of both sets of observations are embodied 

 in the formulae — 



Atmospheric absorption 



At Cairo = 0.187 x Sec. Z.D. in magnitude. 

 At Oxford = 0.253 x Sec. Z.D. in magnitude. 

 Thus the whole effect of the atmosphere at Cairo is to diminish the 

 brightness of stars seen in the zenith by about two-tenths of a magni- 

 tude, and at Oxford by about one-fourth of a magnitude. At an altitude 

 of about 30°, the stars at Cairo will be brighter than in England by 

 about one-fifth of a magnitude, and consequently many more faint stars 

 are just visible at Cairo than can be seen at Oxford. — (Science.) 



Professor Pritchard has printed the photometric observations at Ox- 

 ford, of which the Cairo observations form a part, in the memoirs of the 

 Eoyal Astronomical Society, but the volume has not reached America 

 at the time of writing. 



