ASTRONOMY. 



135 



brifjbter component (wliich Las a sensible proper motion) of tbis optic- 

 ally double star. From measures of position angle be finds 7r=-\-()"A)i)l 

 ±0".013; and from measures of distance, ;r=r+0".112i0".010. Tbe 

 mean result is 7r=+0".104±0".008. 



Parallax 0/ 22398. — xi new investigation of tbe parallax of tbe double 

 star 2 2398 bas been made by Dr. Lamp, based upon observations be- 

 tween May 20, 1885, and Marcb 15, 1887. In tbis be not only obtains 

 a very satisfactory confirmation of bis i^revious value of tbe parallax 

 (0".34) of tbe larger star, but be is able to sbow tbat tbe two stars are 

 at practically tbe same distance. For tbe principal star lie finds tbe 

 annual parallax equal to 0".3520±0".0140; for tbe smaller, 0".3548 

 i0".0131; or for tbe mean, 0".353±0".014. Tbe magnitudes are 8.7 

 and 8.2, respectively, and tbe common proper motion about — 0M7 in 

 rigbt ascension, and -fl".90 in declination annually. 



Parallax of firstmagnitude stars in the northern hemisphere. — Dr. El kin 

 bas completed bis beliometer measures for tbe determination of the 

 parallax of tbe ten stars of tbe first magnitude in tbe nortberu beini- 

 spliere, and summarizes bis results in tbe following table: 



Star. 



a Tauri 



ex Aiirigse 



a Oriouis , 



a Caiiis niinoris 

 (5 Geiiiinoruin .. 



a LeoDis 



a Bootis 



a LyriB 



(X A(iiiilre . 



« tJygni 



Parallax. 



-1-0. IIG 

 -f 0. 107 

 -0.009 

 +0. 26() 

 +0. 068 



+0. 09;? 



+0.018 

 -j-0. 034 

 +0. 199 

 -0.042 



Probable 

 error. 



+0. 029 

 .047 

 .049 

 .047 

 .047 

 .048 

 . 022 

 .045 

 .047 

 .047 



No. of 

 compara- 

 tive stars. 



6 

 2 

 2 

 2 

 2 

 4 



10 

 2 



4 

 4 



No. of 

 observa- 

 tions. 



64 

 16 

 16 

 16 

 16 

 15 

 89 

 ,30 

 16 

 16 



Proper 

 motion. 



0. 202 

 0. 442 

 0. 022 

 1.257 

 0. 623 

 0. 255 

 2. 287 

 0. 344 

 0. 647 

 0.010 



Tbe mean of tbe ten parallaxes gives for tbe mean parallax of a first- 

 magnitude star, -f 0".089 iO'^Olo, a result according well with tbe 

 values deduced by Gyld6n (0".084) and Peters (0".102). 



The probable errors include an estimation of the probable systematic 

 error of the measures. They are therefore considerably larger than 

 those generally assigned to sucb results, which, as a rule, only take into 

 account tbe mere casual error of observation. 



It will be seen on inspection of the table that of the ten stars six 

 may be said to give indications of a measurable parallax, but in only 

 two cases, a Canis Minoris and (v Aquihe, are the values in any degree 

 remarkable, and these confirm closely results of former investigators; 

 Auwers and Wagner having obtained 4-0".240 i0".029and +0".209 

 i0".038 respectively for Procyon, and W. Struve +0".181 i0".094 for 

 Altair. On the otber baud, the next two largest results, those for 



