ASTRONOMY. 373 



selected staudards in tbe twenty-four zones, giving- the positions and 

 ])rovisional niagnitiides, is published, and also a table of twenty-one 

 close circunipolars ranging- in magnitude from 2*2 to 15*7. {Science, 

 "Astron. Xotes.") 



Harvard Photometri/. — M. Th. Wolfl", of the Bonn Observatory, reviews at 

 considerable length (40 pages) the last vohime of the Annals of the Harvard 

 College Observatory, -which contains the photometric investigations of Pro- 

 fessor Pickering and his assistants. M. Wolff has submitted the work 

 of the American astronomers to a minute examination and has estab- 

 lished very interesting relations between the results of the Harv-ard Col- 

 lege meridian photometer and the results of his own work with a Zoell- 

 ner photometer. With the latter photometer the observed star is com- 

 pared with an artificial star, while with the meridian photometer the 

 observed star is compared with Polaris. The two images, one formed by 

 the ordinary and the other by the extraordinary ray of the respective 

 stars, meet in a double image prism and are observed across a Nicol 

 prism. As a check on the work, Polaris was often compared with itself. 

 The magnitudes obtained vary from 1-4 to 2*7, the mean of 630 deter- 

 minations being 1'90 instead of 2-0, the magnitude adopted for Polaris. 

 This discerpancy is inexplicable. The mean of the differences between 

 Professor Pickering's catalogue and M. Wolff's two catalogues is i 

 0-11 magnitudes, or for the logarithm of the intensity ± 0-044. It is a 

 matter for regret that Professor Pickering- did not publish the rela- 

 tive intensities that were the direct results of observation, but pre- 

 ferred to give the magnitudes computed by Pogson's formula, with the 

 constant 0-4. M. Wolfi' very justly remarks that this constant, deter- 

 mined by the observation of telescopic stars, cannot apply to stars of 

 the first six classes; he finds that to establish an agreement with Ar- 

 gelander this constant must be reduced to 0'37, or even to 0-33. Pro- 

 fessor Pickering has endeavored to make his work agree with Arge- 

 lander's by adding + 0-27 to all his results ; but this reduction has 

 altered the discre[)ancies without doing away with them. By reducing 

 the numbers published by Professor Pickering back to the logarithms of 

 intensity from which they were derived, and comparing these results 

 with his own, M. Wolff finds the following mean result : 



W-Wo = 0-84(P- Po), 



which would indicate the existence of an unexpectedly large personal 

 equation. {Bull. Astron., August, 1885.) 



The Oxford Uranometria.* — " The form of photometer Professor 

 Pritchard has adopted is now too generally known to require descrij)- 

 tion. It possesses the high merits of simplicity of construction and use 



^'Astrouoniical observations uiade at tlio University Observatorj-, Oxford, under 

 the direction ofC Pritohard, J). D., F. K. is., F. G. ii., F. 11. A. S., Savilian Professor 

 of Astronomy in Oxford. — No. II. Uraiuindria Nova Oxoniensis. A photometric de- 

 termination of the magnitudes of all stars visible to the naked oyo from the iiole to 

 ten degrees south of the equator. Oxford : At the Clarendon Preas. 



