[iip3 ] 
A Letter from the Reverend Dr Wallis^ Profeffor 
^ of Geometry in the Vniverfity of Oxford^ and 
Fellow of the Roy^I Society^ London^ to Mr. 
Richard Norris,. Concerning theColkdlion of Se- 
cants; and the true Divifion of the Meridians 
in the Sea-Chart. 
A N old enqtiiry,(aboutthe{um or Aggregate of Se- 
r^>2^j-,) having been of late moved a- new r I have 
thought fit to trace it from its Original ; with fuch fo- 
lution as feems proper to it: Beginning firft with the 
general Preparation j and then applying it to the Par- 
ticular Cafe« 
General Preparation, 
1. Becaufe Curve lines are not fo eafily managed as 
Straight lines; the Ancients, when they were toconfi- 
der of Figures terminated (at left on one fide) by a 
Curve line (Convex or Concave,) as jiFKjE, Fig. 1.2. 
did oft makeufeof fome fuch expedient as this follow- 
ing, (but diverfly varied as occafion required.) Name- 
ly, 
2. By Parallel Streight lines, as AT, BG, CH, &c, 
(at equal or unequal diftances as there was occafion J 
they parted it intofo many fegments as they thought 
fit s (ox fuppofed it to be (o parted.) 
3 . Thefe fegments were fo many wanting one, as was 
the number ot thofe Parallels. 
4. To each of thele Parallels, wanting onC:? they fit- 
ted Parallelograms, of fuch breadths as wer^ the In- 
tervalls ("equator unequal^ between each of them (re- 
ipedively ^ and the next following. Which formed an 
Adfcribed Figure made up of thofe Parallelograms. 
I i i 2 5-, And, 
