fay^Thefe intervals are fuch as by calculation they ought 
to bej or to fay, The circles be equidiftant ; For no (euiC 
can diftinguifli the one from the other. And it there had 
been any difference i the Author had fufficiently pro- 
vided ior it, by performing the fame divifions by ftreight 
lines from the center alfo. 
The Computation [of Dr. Wall is) to which the Letter 
refers [the Method whereof is to be feen at large in the 
Philolophical Tranfadions Numb. iii.J is to this pm- 
pofe. See the Figure 12. 
'Take, rve (for injiance) his large brafs Sextant (^n^Z^/^rA 
is one of the hijlruments which he did mojl frequently make 
ufe of^) where A, the Angle [at the Center) is Minutes ^ 
to be divided into f equal parts ^ by a Streight Diago- 
nal, obliquely cutting [in the Limb) 6 Concentrick Cir- 
cles; (the length of the Ray, toeachofwhich^ we are to 
enquire.) 
The of that Infrument is (more than) 6 foot; 
and the breadth of the Limb (cutt by the Diagonal) is 
fomewhat more than half an Inch \ that is^ fomewhat more 
than part of the Radius. 
We will allow it to be at lefl ihp^rt Radius, {or 
even fomewhat more than fa:) and^ accordingly^ O, the 
Obtufe angle at the Bafe (contained by the Diagonal and 
the fhorteft Ray, or that of the In-moft Circle) 172 de- 
grees .* And therefore Yfthe Acute ang-le at the Bafe,)cQH' 
tained by the Diagonal and the Longeft Ray, (or that of 
the Out-moft Cw/^ , ) will {becaufe of at the C en-- 
ter , of f \ ) bey"", ff : A?id that at the Second Circle 
{next to it ) will (becaufe, hercy A = 4' J be 7°, T6' : And, 
at the thirdy 7% /7'; Andy at the fourth, 7% jS' : And 
, at the fifth (which is next to the In-moft) y"", jg'. 
Then (by that Cafe of Trigonometry . where. The two 
Angles at the Bale being Given, with a fide Oppofite 
to one of themi we are to Find that oppofite to the - 
other :j 
