ASTRONOMY. 191 



motion is slow and can be represented by a simple formula of interpolo- 

 tiou, partly because it has been very frequently measured by almost all 

 observers of double stars. First, three normal places were formed which 

 represented the distances and i)08ition angles observed since 1815, and 

 an angle of position from Bradley's and W. Herschel's measures. 

 From these and the ratio of the sector to the time, formuhie for computing 

 distance and position angle as functions of time by means of the eccen- 

 tric anomaly were derived and an ephemeris computed from 171S to 

 1900. With this ephemeris all individual observations by every obser- 

 ver were compared and the mean error determined for every observer 

 within a period during which he might be supposed not to have changed 

 his way of measuring. Every observer is now followed from one period 

 to another and the changes in the mean error determined, whereby vari- 

 ations in his systematic error reveal themselves. 



Dr. Seeligee has maxle an elaborate examination of Madler's 

 measures (A. I!^. 2288). Madler's distances appear to be considerably 

 less accurate than O. Struve's, while his position angles do not appear 

 to have larger mean errors than those of O. Struve. 



The most important series of double-star measures published since 

 Mensurce micromeiricw is that given in Volume IX of the Pulkova Ob- 

 servations, comprising the work of Otto Struve with the 15-inch 

 refractor since about 1810. An elaborate introduction details the 

 observations of artificial double stars and the method of applying the 

 corrections thus obtained to the measures of real stars. Section I is 

 devoted to the re-measurement of a large number of the most interest- 

 ing of the stars forming the catalogue of the elder Struve. Section 

 II contains the measures of nearly all the stars of the revised edition 

 of the Pulkova catalogue of 1850, and about thirty additional pairs dis- 

 covered subsequently {01 515 to 517). The only other systematic observa- 

 tions of these stars were made by the late Baron Dembowski about 

 18G0. As many of these pairs are rapid binary systems, and nearly all 

 of them interesting from the closeness and inequality of the components, 

 the Pulkova measures, giving earlier epochs, are specially valuable. 



A valuable contribution to the literature of this department, and sec- 

 ond to none in practical value to the observer, is Flammarion's "Cata- 

 logue des Etoiles doubles et multiples en mouvement relatif certain." 

 This work contains a complete list of all double stars the components of 

 which have shown any decided change either from orbital or proper 

 motion, with all the published micrometrieal measures down to 1878, 

 arranged in chronological order, and notes as to the character and extent 

 of the motion, the most recently computed orbits of binaries, etc. As a 

 working list for the practical observer it is si>ecially valuable, since the 

 stars which most need observing can be at once selected. 



The " Haud-Book of Double Stars," by Messrs. Crossley, Gled- 

 hill, and Wilson, published in 1879, in addition to an extensive cata- 



