ASTRONOMY. 



By Prof. Edward S. Holden, 

 Director of the Washburn Observatory, Wisconsin. 



INTRODUCTION. 



The record of astronomical progress for 1881 must necessarily be a 

 very condensed summary. It is to be remembered that this review is 

 not primarily intended for astronomers, but is specialy addressed to 

 the correspondents of the Smithsonian Institution. For bibliographic 

 information the reader is referred to Darboux et Houel's Bulletin 

 des Sciences Mathematiques et Astronomiques (monthly, Paris), to Nature 

 (weekly, London), to IScience (weekly, New York), to Copernicus^ 

 (monthly, Dublin), to the Observatory^ (monthly, London), and to other 

 standard journals. Free use has been made of reviews by writers in 

 these and other periodicals. 



NEBULA AND CLUSTERS. 



PJiotographs of nebulw. — M. J. Janssen calls attention to the effect of 

 short and long exposures upon the negatives which are obtained. Pho- 

 tographs of the same nebula will not agree unless the same conditions 

 of exposure are narrowly observed. In proof of this the photographs 

 of the solar corona taken at Siam in the eclipse of 1875 are referred to : 

 The nebulosity, so to speak, of the corona gave different impressions 

 upon sensitive plates which were exposed during times expressed by 

 the numbers 1, 2, 4, 8 ; and it must be inferred that the changes in the 

 height of the corona are to be attributed to the times of exposure, in- 

 stead of to actual variations in the extent of the phenomena. M. Jans- 

 sen proposes to take the photograph of the image of a star, or nebula, 

 a little out of focus. In this case the photograph is a little circle of 

 sensibly uniform opacity, and one can compare the opacity of the pho. 

 tographs of different stars, and connect the degrees of opacity with the 

 I)hotometric i^ower. — Comptes Ixendus. 



The Publications of the Washburn Observatory No. 1 contain a list 

 of 23 new nebulae, mostly faint. 



Cluster measurements. — H. C. Russell, director of the observa4;ory of 

 Sydney, has made a micrometric examination of the cluster h. 3276= 

 G. C. 2144, which gives the positions (and magnitudes) of 144 stars. 

 One of these is an interesting red star. The pai)er is accompanied Dy a 

 map of the cluster made by Mr. Russell, himself, by a process whict he 

 describes as extremely easy for any one to execute. 



