142 KECOKU OF SCIENCE FOR 1887 AND 1888. 



inally of the third magnitude; and each in turn declines by about half 

 a magnitude and recovers within a few days, yet so that the general 

 preponderance, during a cycle of several years, remains to the same 

 star. Miss Gierke suggests that simultaneous variation in the color of 

 neighboring stars may lead to the discovery of their physical depend- 

 ence. 



Mr. G. F. Chambers has prepared a catalogue (still in manuscript) of 

 seven hundred and eleven red stars, brighter tlian the eight and one- 

 half magnitude, the result of observations made from 1870 to 1880; 

 less than twelve stars, according to Mr. Chambers, can properly be 

 termed carmine or ruby. 



STELLAR PHOTOMETRY. 



The magnitudes of the standard stars of the British, French, German, • 

 Spanish, and American nautical almanacs have been rediscussed by 

 Professor Pickling, and his results will probably be adopted in future 

 issues of the French, Spanish, and American works. The plan pro- 

 posed was, that the magnitude adopted for each star should be the 

 mean of those derived from the Harvard Photometry, the photometric 

 observations of Wolff, the Uranometria Oxoniensis, and the Urano- 

 metria Argentina. The list published embraces 800 stars, and of these 

 the magnitudes of all but 04 depend upon at least two and generally 

 upon three authorities; 132 stars being common to all four of the 

 adopted standard catalogues of brightness. 



A ''wedge-photometer," constructed under the direction of Professor 

 Pritchard for the Uarvard Observatory, has been submitted to a careful 

 examination by Professors Langley, Young, and Pickering, and' it ap- 

 pears from Professor Langley's investigation of the wedge, by means 

 of his bolometer, that there is a selective absorption of light throughout 

 the wedge; feeble in the more luminous portion of the spectrum, but 

 of such a character that, broadly speaking, the transmiss'ibility always 

 increases from the violet toward' the red, increasing very greatly in the 

 infra-red. These results have been confirmed by Professor Pickering's 

 experiments, and they emphasize the danger, already recognized by 

 Professor Pritchard, of employing an instrument of this kind in the 

 observation of deeply-colored stars. 



From a comparison of the star-magnitudes of the Oxford Uranometry 

 with those of Wolff's second catalogue, and with those of the Harvard 

 Photometry, Professor Pickering has found that the Oxford magnitudes 

 are, on the average, less than the Harvard magnitudes for stars down 

 to the third magnitude, but greater for the fourth and fifth, and less 

 again for stars below the sixth. The Harvard catalogue differs less 

 from those of Wolff and Pritchard than the two latter do from each 

 other. 



