35$ Mr. Wollaston’s Defcrtption of a 
Bat It may, perhaps, he of fervice to aflronomy, or at leafb 
Bot unacceptable to thofe gentlemen who ufe the Rhombus, 
that I fhould fubjoin another formula (contrived for me the lad: 
fum tiier by my Son, now Mathematical Lefturer at Sidney 
College, Cambridge) for invedigating the comparative right 
afcenlions 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 lcale, 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 
63° 26' 6 // ) be called - - - - a 
The diagonal LL (whofe extent, that is, what portion of 
a great circle it comprehends, mud: be known to theobferver) 
be called - ^ 
The larger interval obferved between the paflage of a dar 
by an oblique and the horary wire (as b c) • - - m 
The fmaller ditto of the fame ftar (as c d) - n 
1 
The larger ditto of another dar (as /3 y) *» - p 
The fmaller ditto (as y J) - - - v 
rn^-n 0 
with a parallel of declination : call this q 
The angle q being thus found, then 
2 . n v x fm ’ a +9 V cof. q. — difference in declination between the 
& x fin. a 1 
two points on the vertical wire where 
/ thofe 
