ASTRONOMY. 



135 



brio-liter componeut (which has ii iseusible i)roper motion) of this optic- 

 ally doable star. From measures of i)osition angle lie finds 7r= -|-()".UUL 

 ±0".l)13; and from measures of distance, /t== + 0'M12±0".010. The 

 mean result is ;r=+0".104±0".008. 



Parallax of 2 2398. — A new investigation of the parallax of the double 

 star 2 2'598 has been made by Dr. Lamp, based upon observations be- 

 tween May 20, 1885, and March 15, 1887. In this he not only obtains 

 a very satisfactory confirmation of his previous value of the parallax 

 (0",3-t) of the larger star, but he is able to show that the two stars are 

 at practically the same distance. For the principal star he finds the 

 annual parallax equal to 0".3520.-t0".014(); for the smaller, 0".3548 

 ±0".0131; or for the mean, 0".353±0".014. The magnitudes are 8.7 

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

 right ascension, and 4-l".90 in declination annually. 



Faralla.v of first-magnitude stars in the northern hemisphere. — Dr. El kin 

 has completed his heliomeler measures for the determination of the 

 parallax of the ten stars of the first magnitude in the northern hemi- 

 sphere, and summarizes his Msults in the following table: 



Star. 



a Taiiri 



a Anri^ji' 



(X Orionis 



ex Cauis minoris 

 fS (ieniiiioriiin .. 



a Leon is 



(X liootis 



a Lyrai 



a A(inil;c 



« Cygui 



Parallax. 



Probable 

 error. 



+0. IIC) 

 -fO. 107 

 -0. OUl) 



+(». 2()(; 

 -fo. m)fi 

 +0. 09:} 

 +0. ois 

 -f 0. o:54 

 +0. 191) 

 -0.042 



±0. 029 

 .047 

 . 049 

 .047 

 .047 

 .048 

 . 022 

 . 04') 

 .047 

 .047 



No. of 

 compara- 

 tive stars. 



No. of 

 observa- 

 tions. 



2 

 2 

 2 

 4 



10 

 2 



4 

 4 



(54 

 16 

 16 

 16 

 16 

 15 

 89 

 30 

 16 

 16 



Proper 

 motion. 



0. 202 

 0.442 

 0.022 

 1. 257 

 0. 628 

 0. 2.55 

 2. 287 

 0.344 

 0. 647 

 0.010 



The mean of the ten parallaxes gives for the mean parallax of a first- 

 magnitude star, +0".0S9 i0".015, a result according well with the 

 values deduced by Gylden (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 such results, which, as a rule, only take into 

 account the 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 oidy 

 two cases, a-Canis Minoiis and (y Aquihx^, are the values in any degree 

 remarkable, and these confirm closely results of former investigators; 

 Auwers and Wagner having obtained 4-0".240 ±0".029 and -f 0".299 

 i0".038 respectively for Procyon, and W. Struvo +0".181 i()".094 for 

 Altair. On the other hand, the next two largest results, those for 



