ASTRONOMY. . 349 



disceru no trace of the nebulosity ; aud D' Arrest also failed to see it 

 when observing the star with the Copenhagen refractor on the 25th of 

 January, 18G5. Nor has it since been seen until quite recently, when 

 it was noticed by Mr. K. Tarrant, using a 10-inch 'With' reflector, at 

 Pinner, Middlesex. D'Arrest had noticed a small star of less than the 

 12th maguitude, a little preceding the II th magnitude star previously 

 mentioned, and nearly on the same parallel with it. When the nebula 

 was first seen by Mr. Tarrant (on the 14th of March, 1885), it was 

 lengthened in the direction of a circle of declination, and this faint star 

 was at its following edge. The first known instance of this kind was 

 that of the nebula near e Tauri, discovered by Mr. Hind in 1852, sus- 

 pected to be variable from not having been seen before, and afterwards 

 proved to be so, becoming invisible even with very powerful telescopes, 

 and subsequently reappearing." {Athenceum.) 



ASTRONOMICAL CONSTANTS, ETC. 



A neic determination of the nutation constant. — "Dr. L. de Ball has 

 emi^loyed for this determination the right ascensions of three polar 

 stars {a and d Ursse Minoris and 51 Cephei), observed at Pulkowa by 

 Herr Wagner, part of which have already been employed by Herr Ny- 

 ren in his researches concerning the constant of aberration." {Bulletin 

 Astron., i, p. 202.) Although these observations, which were made be- 

 tween 1861 and 1872, embrace only a little more than half a complete 

 period of nutation, their precision is such as to justify Dr. de Ball's 

 attempt. He has had at his disposal 934 eyeand-ear observations and 

 933 chronograph observations. The mean error of an observation is 

 nearly the same for the two methods. By introducing as unknown 

 quantities the corrections to the mean right ascensions of the three 

 stars to the nutation constant (Peters) and to the aberration constant 

 (Struve), and also the parallaxes of the stars under consideration. Dr. 

 de Ball has attained the following results : 



Correction to the nutation constant Jn — 006 -1; 0-012 



Correction to the aberration constant Ja +0-043 ^0-011 



Parallax of a Ursai Minoris -f 0-015 J^ 0-015 



Parallax of 51 Cephei +0 027 ^J^ 019 



Parallax of d UrsiB Minoris +0-034 ^ 0-017 



8 8 



R. A. (18650) of a Ursae Minoris (eye and ear) Ih ym 38-706 ^i; 043 



R. A. (1865-0) of a Ursa Minoris (chronograph) 39-057 -j- 0-051 



R. A. of 51 Cephei (eye and ear) e^ 36™ 11-723^^0-026 



R. A. of 51 Cephei (chronograph) 12-012 -|- 0-027 



R. A. of d Ursne Minoris (eye and ear) 181^ 15'" 53-084 i 0-020 



R. A, of d UrssB Minoris (chronograph) 53-363 ^ 0-020 



"The six values of the correction /In furnished by the three stars do 

 not show a very remarkable agreement : 



Eye aud car. Chronograph. 



a Ursas Minoris — 0"-062 — 0"-011 



51 Cephei +0"028 +0"-003 



5 Ureai Minoris _0'-016 +0"-039 



