[ 5 6 ° ] 
Chart, were analogous to the logarithmic Tangents 
of the Half-Complements of the Latitudes. And, 
fecondly, To find a Rule by which the Tables of 
meridional c Parts might be computed from BriggsV, 
or the common logarithmic Tangents. The former 
of thel'e the Doctor has clearly and elegant. y proved : 
But he has given rather too few Steps to fhew as 
clearly the Inveftigation of the latter. 
Indeed in many of the Treatifes on Fluxions, it is 
fiaewn how to inveftigate a Rule to find the meri- 
dional Parts to any Latitude : Bur, to underftand 
thole Methods, requires fome Skill in algebraical 
and fluxionary Computations 5 neither of which are 
neaflary in this Bufinefs, by keeping to the Doctor’s 
Principles, as will be evident from the following 
Articles; fome of which are already well known; 
yet it was thought convenient to annex them to this 
Difcourfe, by 
Tour moft humble Servant , 
John Robertfon. 
Article I. If the Circumference of a Circle be di- 
vided into any Number of equal Parts by as many 
Radn, and a L ne be drawn from the Circumfe- 
rence cutting thoje Radii, fo that their Tarts in- 
tercepted between this Line and the Centre be 
in a continued decreafing geometric ProgreJ]ion\ 
then will that interfelting Line be a Curve , 
called the proportional Spiral , and will interfe£t 
thofe Radii at equal Angles. 
I t .»# 
This 
