24-3 G E R A R D [ R E G N E R 1 F C K. E N 5 



« Thainanner in whicli Ihcseresulls have been deduced from the Greenwich Observation« 

 « will be easily understood fiom ihe annexed serics of piaces of Ihe pole-slar and a, Lyrae. 

 « Biit it may be iiroper to makc some remarks on the computations for euch year. " 



Itaque sepaialim iraclat observationes Greaovicenses annorum 1813, 1814, 1815: re- 

 jicit 3utem annos 1812, 1817. 



« In instituling the abovo examinalion of the obscrvations of the mural circle , my 

 « only object has been lo endeavour lo Ihrow light on a very diificult subject. There 

 « cannot be a doubt Ihal Mr. Pond's melhod of deducing the index correction is most 

 « proper for observations in general , such as the polar distances of the sun , raoon and 

 « planets, etc. But when used for parallai , there appear too many sources of error 

 <( mixed up together , lo ascerlain their precise eilect on the mean index correction, " 



« The only method of examining the capabihly of the inslrument for Ihis purposc 

 « seems to be Ihat of comparing the difFerences of the polar distances of two Stars in the 

 « opposite seasons, in the manner Ihat I have done for the pole-slar and et, Lyrae. The- 

 « re are however raany obstacles Ihat will circuinscribe both ihe choice of Stars and num- 

 « her of observations. " 



Tractat aulem deinceps annum 1816. Tandem, anleaquam profert tabellas , quae ob» 

 servationes continent Greaovicenses, ita scriptionem claudit: 



« It would not be right to conclude Ihese remarks without noticing one circumstance 

 « Ihat shows in a striking raanner ihe skill with which Ihis Instrument has been con- 

 « slructed and supported. There appears nolhing by which we can State wilh cenainr 

 « ty ihat ihe iudex error of Ihis inslrument changed from April 16, 1814, lo Ihe end 

 « of the year , and also from May 24 , 1815 , to the end of Ihe year. This permanency 

 « of the mural circle in summer and winter surpasses considerably Ihat of the fixed te-. 

 « lescope used for a, Cygni, In Ihat instrument a change, as has been remarked else^ 

 K where , took place , amounling lo several seconds belween Jaüuary and June. ". 



§ 14. 



Interim Pondius quaestionem repetiit 14 Novembris 1822, et, ni fallor , prorao- 

 Vit (»). 



« My former experimenis wiih a fixed telescope upon « Cygni have always appeared 

 « to me so decisive , as to render hopeless any farther altempt lo discover its parallax ; 

 « but rcspecling thal of « Lyrae, my observations wiih the mural circle were not 



<( equaJ- 



(*) Fldl. Trans. iSaS. P. I. p. 53. Tom. CXIII. Titulus est: On the parallax of s. Ljrae. Bj; 

 J. Poud. Esq. Astronomer Royal. F. R. S. 



