(58' C'F R A R D 1 R E G'N E R I POCKEN» 



uiidc : 



S, — S = 3 T sin. « COS. a' scc. N' =r — 2wt 



t : 



X = (S,— S) : 2sin. d' cos. a' sec. N'^ — (S, — S) : 2»t 



Sed hoc loco , quod ad praxia attinet , animadvertendum est, Pondium utramqiie 

 slellnm suam non tarn cum filo fixo , quam ope fili cum alia Stella fisa comparasse. 

 liac aulem de re ipse ita loquatur : {*) 



I do not attempt to refer the position of llie slar , whose parallax is to be asccr- 

 laiiied , to any point delermined by a level or pliimb line , but by means of a microme- 

 ter wilhin the telescope I measure only its difTerence of decliiiation from some other 

 Star which passes througb the same field; the telescope itself being sccurely fixed on' 

 a stone pier. The sta? chosen for the purpose should differ as much as possible in 

 ri°-ht ascension from the star , whose parallax is to be invesligated , that the resulls 

 may be affected by the sum of llie parallases of bolh stars. It should likewise be 

 sufficiently bright , to be visible even when it passes the meridian at noon : olherwise 

 the observations must necessary be subject to a period of interruplion at the very time , 

 they would be of tlw most importance. Should the difference of the two stars 

 exceed 8 or 10 minutes , it will be advisable to apply a double micrometer to the 

 telescope ; that is a micrometer having two moveable wires , such as have been made 

 ,r for some years past by Mr. Troughton." 



Itaquehoc modo Aquilae ot, comparavit cxanPegasi l, quae eandem ferme declinationem 

 habet, sed adscensionem trihus horis cum quadraate majorem. Ita scilicet factum est, ut 

 neque hyeme ante solis occasum neque aestate post solis ortum Iransiret : imo factum 

 est, ut nullus observationum error oriretur, quotiescunque eodem die, id est intra qua- 

 luor horas, utrumque sidus esset observatum. Ecce Vobis scema quatuor e 54 obser- 

 vationum , in quibus parallaxis debuit gtellarum distanliam mutuam augere ( f ) •' 



Aquilae * — Pegasi /. 



Reducta in arcum. Reducta ad 1817. 

 i'55",65 i'49",95 



52, 62 48, 21 



53, 90 49, 61 

 52, 63 48, 55 



t*) Philosophical Transaclions , 1817. Tom. CVIL P. 11. p. 354. 

 ( t ) Phil, Trans , 1818. CVllI. 11, 477. 



