fi 1260-1263. l'he prominence, which iR due in many astronoiiiicsl re- ortlcr to restore this uniforiiiify , which is otiviously of the searches to the long and excellent series of the Greenwich iiiost esseritial iiriporhiicbe, 1 have rel'errctl all the otiser- mericliorial oliservations, gives to any changes of the instrri- vatioiis to the Circle reatlirigs. which corresporrtl to the Naclir nients, by means of which these ohservatioiis are procurecl, observations of the wire. It iiiight have heen tlcsirahle to a higher and more general importance, than they woulcl other- get rid, as much as pnssilile, of' pere~nalecpitions in the wise possess. Hence the interest, with which astrononicrs reading of iiiicroscope - iiiicronieters etc. hy iisiclg for each are wont to regRrtl the construction and cfhiency of any new observer his own Zenithpoints. A closer inspec:tiori sjiotv,, instrunient of superior pretensions, is greatly enhanced in however, that, owing to several ciiwes, this (:nurse is for the case of the powerful Greenwich Transit Circle, and the the past observations inipracticable. I have 'coiiserperitly asiral question, concerning the degree of correctness, which considered it best to adopt the same periods of uri;iltered the results of a new apparatus have attained, acquires addi- Zenithpoints, as have Iieerl used in the Greenwiclr rechictioris. tional claims to be answered. As I an1 not aware, that a The values of the corrections, which it was accordingly seces- strict determination of this point has yet been attempted, 1 sary to apply to the single ohservations, fluctuate I)ct\veeri shall here niake it the suhject of inquiry with reepect to -fO"45 and TO"71. Polar Distances, so far as it may be safely decided from The correction for fl ex u re, which has heen eriiployed the data, which arc furnished by the printed obsevations of' in the Greenwich reductions, is incorporated in the tiible for the first four years. division errors. The amoimt of the correction is not NtatecI and the appendix to the volume for 1852, to tvbich tbe § 1. reader ie referred, does not supply the deficiericy. Prorii The stars, which 1 bave selected for the purpose of the tables it appears however, that the adopted correction irr reducing all their available observations to some conimon 1851-1852 is +0"73 sinz and in 1853-1854 +O'50 sittz, epoch and of comparing the single results with each other, where Z denotes the southern Zenith Distance. The latter are those of the enlarged catalogue of the Nautical Almanac coefficient is the mean of the three deterniinafions of the (so far as it concerns Greenwich and with the exception of horizontal flexure, taken Iiy help of the colliniators arid nien- the star vorioois, of which there are no observations), the tinned in the appendix. But I caniiot discover the origin of clock-stars given in the Greenwicb volume fur 1854 and, the other coefficient, unless it he assunied that iri coiiibiiiing besides a few others of special iatereet, all those, which the two earlier deterniiriatioris cloulile weight has heen allowed have been observed at least ten time8 during the four years. to the second. In order to restore uniforniity, the ohser- That the observationsl of these stars niay allow of a strict vations of t.851 - 1852 have been corrected, c1o that they comparison with each other, it is first neceesary to Clear the contain the same flexiire correction +O"jO sfit Z, which is single results, which are given in the Greenwich volumes, *) employed in succeeding ,years. of the systematic errors introduced by the w 9 n t of u n i f o r - The reduction, which the rcflexion - observalioris require ni i ty in the deduction of the adopted Z e n ith p IJ i n t s. In 011 eccount of the divergency of the norilia18 at the $ace of the quickoilver ourface arid at the Circle's centre, *) In the aection ,,Mean North Puler Dietansce of atare deduced has also been applied, a reduction, which, so far as I know, frum each day's observation." has always heen neglected in British oliriervatories. In the f) The prcnent payer W86 originally writtdd with a view to its bein& printed in England, HI the yrolmlile length aeemed tii t'orliid ite ineertiun in tht Aetron. 'Nwhr. The c*lrcumhnL!r, which yretented it frum bdng pulilidhed iii the wily first intended, render any essential changes undihitakde. The rluthor huyee therefire, thht thid will be bnme in mind, if miwe poitit8 nrc found ru be treated in rather P dilfercnt mitniier Proin thnt, which he would otherwide had deemed most ruit;rlilo 53r Hd. I2 179 Nr. 1260. construction of the present Greenwich Transit Circle the quick- Alm. and clock-stars excepted) and if only the exact means silver is carried by an apparatus, which keeps it nearly at of the dates of observations were given. an equal distance of about fronr the centre; the correction 96". The observations have then further beeri reduced for amnunts consequently to sh +0"16 2. precession and proper motion to 1855.0, which epoch has In order that the Greenwich annual results may be heen chosen with a view of preparing for the future addition hrought up properly to some comnion epoch, they require, of the results of following years. For the same reasou the besides the reduction for the intervening years, two minor correction of the colatitude has also been employed, which corrections. The first of these is owing to the circum- has been deduced in the volonie for 1854, so that the reduc- stance, that the observations are, or profess to be, reduced tions contain the eame colatitude J8°31'22u00, which is to Jan. 1 Greenwich mean noon and that consequently there adopted at Greenwich from the beginning of 1856. is every fourth year a break of continuity in the progress of the epochs. For tlie future this source of needless in- After applying the different quantities just mentioned, accuracy is happily stopped, since in the Naut. Alm. for and excluding those observations, which have been found 1857 Bessel's reckoning is adopted, according to which the too discrepant and which will he spoken of presently, I have sidereal year begins at the moment, when the mean AR. of taken the means and, after comparing with them the single the Sun is = 280'. Front 1857 to 1860 therefore this cnr- results, have deduced the probable errors of the latter. rection will only be needed by those star-places, which are There seems to be no fixed rule laid down at Greenwich reduced by means of the Greenwich day numbers. - The tor the exclusion of discrepant observations; at least in some second of these minor corrections has its origin in the cases observations are without any apparent special reason neglect of proper motion in making the reductions to the he- rejected, which are less discrepant than others, which are ginning of the year for the stars, which are not contained retained. Since niistakes have obvinusly soinetinres happened in the Naut. Ah. This neglect does no harm in the annual and since therefore sonre assumption in drawing the line catalogues, as the fraction of the year is there given, which hetween less accurate observations and mistakes cannot be corresponds to the mean date of the ohservations. But it is avoided, 4 have considered 4" to be a fair liitrit for stars otherwise in the Greeiiwich general catalogues; for , since of lcss than 70" or 73" %. D., so that, in their cases, every the annual variations, which have been iieed in their con- resiilt has heen rejected, which differs niore than 4" from struction, include proper motion and yet the deficiencies for tlie riieari of all the results, the discordant one included. lo the respective fractions of the different years are not supplied, conformity with this rule, ten observations have been excluded the accuracy of the nrean places is by this oversight sonie- tiesides those already thrown nut in the Greenwich volumes; times very sensihly affected, as may he seen from a few but of the latter on the other hand four have heeii retained. instances in the last Greenwich general catalogue (Cat. of The results for all the stars selected have then been 1576 stars for 1850), iu which the follnwiiig places require arranged in the following table in the order of increasing on this account the corrections North Polar Distances, D and R denoting the results of the in AH. inSPD. - - direcl and reflexion-observations, n their nunilier und 8 their No. 46 VCassiopeae -0' 13 -0"15 prohable errnr as fnund hy comparing the single obser- 47 B. F. 75 -0903 -It00 vstions with their means. In a few cases of large proper 159 Piazzi 11. 123 -0909 +I902 niotion and in all eases, where the number of observations 770 1830 Groonibridge -0711 -1982 etc. is less than 10, these prohahle errors are omitted. - The Of course under the circumstances it would be niuch resultiiig North Polar Distaiices Sub Pola are nf course to better, if proper motions were disregarded entirely (the Naut. he considered negative. NO. AR. Star D 1855,O 11 6 R n 6 -- - -7 - Lc --- 1 20b 9" A Ulnae niin. 1" 7' 27"79 ?I O"548 27"60 'LO O"543 s. P. 27982 31 570 28 t 04 11 525 2 17 a Ursae nrin. 1 27 48r5Q 259 607 48-93 28 784 s. P. 48 t 96 306 622 48 * 36 19 916 3 6 31 51 Hev. Cephei 2 44 50976 31 578 52t61 2 s.