2$o Mr. Wollaston's Defcrtption of a 



But it may, perhaps, be of fervice to aflronomy, or at leaft 

 not unacceptable to thofe gentlemen who ufe the Rhombus, 

 that I Ihould fubjoin another formula (contrived for me the laft 

 llimmer by my Son, now Mathematical Le6lurer at Sidney 

 College, Cambridge) for investigating the comparative right 

 afcenfions and declinations of ftars obferved by it, when the 

 inftrument is not placed truly in the plane of the equator. I 

 was led into wifhing for fome fuch formula, in confequence of 

 an ingenious Paper, kindly communicated to me by Sir H. C. 

 Englefield, Bart. F. R. S. giving an account of his method 

 of doing it by a fcale and figure ; which, though very eafy 

 when one is provided with fuch a fcale, appeared to me to be of 

 lefs general ufe than by calculation ; and I do not know that 

 any thing of the kind is to be met with in any publication. 



Let the angle DLL, fig. 2. (which, by conftrudlion, is 

 6f 26' 6'') be called . - - . ^ 



The diagonal LL (whofe extent, that is, what portion of 

 a great circle it comprehends, muil be known to theobferver) 

 be called - - - - _ j 



The larger interval obferved between the paffage of a flar 

 by an oblique and the horary wire (as b c^ - - m 



The fmaller ditto of the fame flar (as c d) - n 



The larger ditto of another flar (as jQ y) • - jt* 



The fmaller ditto (as y J) - - - v 



Then — ^ — = tangent of the angle which LL makes 



with a parallel of declination : call this (^ 

 The angle q being thus found, then 



^ . «c^>x in. g — £ ^^^^ _ (jjffgj-gj^j^g \^ declination between the 



two points on the vertical wire where 



thofe 



