Royal Astrojiomical Society. 60 



may be affected, by reason of the small optical power of the tele- 

 scope and other matters inseparable from an inferior instrument. 

 Hence they may be considered to be quite insignificant : taking them, 

 however, as they are, and comjiaring them with the azimuth errors 

 of the large transit in the corresponding period of the years 1841-42, 

 the fluctuations of the large instrument turn out to be five times as 

 great as those of the small one ; a convincing proof that the cause of 

 the changes hitherto remarked is not in the ' hill on which the ob- 

 servatory is built.' The above list of errors in azimuth may also 

 convince observers that they may themselves rub down unadjustable 

 Ys to limits which will be abundantly within easy calculation (and 

 with transits, too, without micrometer wires). 



*' The Ys of the large transit having been erected, every screw 

 about the instrument was tried, to make sure that it was doing its 

 duty : a number of the smaller ones (which seemed to be made of 

 brass wire — drawn brass, not cast brass) were found quite rotten ; 

 these were replaced, and a good many new ones introduced about 

 the sliding tubes at the eye end ; handles for moving the instru- 

 ment, and acting only in the plane of the meridian, were added ; and 

 then, as the line of soldering of the telescope was beginning to 

 show symptoms of oxidation, the instrument was painted. A nadir- 

 pier and mercury-trough have been established, and a collimating 

 eye-piece of peculiar construction, which for perfect vision seems to 

 leave little to be desired, and reveals almost every affection of the 

 instrument. On account of some of its revelations, the fixed wires 

 have been removed, and five in their place mounted on the micro- 

 meter-frame. I propose to examine the errors of collimation and 

 level every night, before and after the observations, as shall be found 

 necessary, and am now engaged in trying to cure the reversing- 

 carriage of a trick it has got of throwing the instrument to the west 

 during reversal. Collimating lenses, of the full aperture of the 

 object-glass, for marks on the boundary wall, are also being put up, 

 as the old semi-collimating semi- meridian m.arks are now seldom 

 seen, on account of the increased smoke of the city ; and when they 

 are, the 6* 5-inch aperture of the transit must be reduced to 2 inches, 

 and the eye-piece pulled out so far as to make the wires very indi- 

 stinct and unsteady." 



Oxford. 



The Radcliffe observer has lately published his seventh annual 

 volume. This consists, like the preceding volumes, chiefiy of ob- 

 servations of circumpolar stars contained in Groombridge's Ca- 

 talogue. 



It is not necessary to dwell upon the merits of Groombridge's 

 Catalogue, one of the most laborious tasks ever undertaken by an 

 amateur, as well as one of the most useful. His transit circle, 

 though i^erhaps rather weak as a right ascension instrument, was at 

 the time of its construction, and for many years after, the most per- 

 fect instrument in existence for determinations in north polar di- 

 stance. On this account, and considering that the time elapsed 



