COMMENTATIO ASTRONOMI C \. 195 



ji dilTerent plumb-Iines ; since the various adjustments of Ihe same point agreed with each 

 « olher, within less than half a second." 



« Having then , froin such trjals , sufficient reason to cönelude , thal these second 

 ..« luiexpecled deviations of ihe stars were not owing to any imperfeclions of my in- 

 « slruments; after I had settled Ihe laws of the aberrations arisiiig from the motion of 

 « light, etc.; I judged it proper to conlinue my observalions of the same stars; hoping 

 « that , by a regulär and longer serips of them , carried on thro' several succeeding 

 « years, I might , at length , be enabled to discover the real cause of such app^rent 

 « inconsistencies. " 



« As I resided chiefly at Wansted , after my sector waserected there in the yoar 1727 

 « tili the beginning of May 1733, when I removed from thence to Oxford: I had, 

 « during my abode at Wansted, fcequent opportunities of re>ieating my observations ; 

 « and thereby discovered so many particulars relaling to these phaenumena , that I 

 « began to guess what was the real cause of them. " 



« It appeared from my observalions , that , during this inlerval of time , some of the 

 ■« stars near the solstilial colure , had changed their declinalions 9" er 10" less, than a 

 « precession of 50 ' would have produced; and, at the same time, that others near Ihe 

 « equinoclial colure had altered theirs about the same (juantily more , than a like pre- 

 j( cession would have occasioned : the north pole of the equator seeming to havc ap- 

 « preached the stars , which corae to the meridian wilh the sun , about the vernal equi- 

 « nox and the winter solstice; and lo have receded from those , vvhich come to the 

 :« meridian with the sun , about the autumnal equinox and the summer solstice. " 



Ergo comparavit observatas varialioneg cum nodi lunaris situ. Sed hae etiam aliud 

 quid, tanquam axeos terreslris nutalionem , requirebant. Anno 1738 satis sibi persuasum 

 iiabuit , partem motus , nisi totum , esse tribuendam actioni lunae in aequatorialem tel- 

 luris cingulum ; sed quo certior fieret de hoc axeos motu , observaliones per univer- 

 sam nodorum revolutionem voluit coutiuuare , qua elapsa , cum voluptate Stellas in sua 

 loca reduces vidit. 



Jaminvocavit Machinium, qui theoriam persequerelur hujus nulationis. Sequelas islius 

 hypotheseos indagavit, iisque vidit observaliones respoiidere. Nonnulla aulem praemonet 

 ■de hac comparatione , in qua praecessionem 1° per 71 1 annos, obüquitatem 23° 28' 30" 

 per 20 annos constantem, aberrationem 40", epocham aulem 27 Illarlii 1727, assumsit. 

 Porro agil de sectore et ralione observandi : errorem raro 1" siiperare afSrmat. 

 Dein observaliones cum hypothesi comparalurus paucos dare cupit , at quae rem con- 

 ficiant. Frequentissime observavit y Draconis, slellam scilicct Wansteadiae zenithalem. 

 Punctum in limbo, ad quod referuntur observaliones, est 38° 25' distantiae polaris. Se- 

 queas tabella exhibet : 1) tempus observatioms; 2) numerum secundorum , quibus lo- 



Bb 2 cus 



