C 99 ] 
fines of the fucceffive degrees, and parts of decrees 
intended to be put on the fcale, defending ordertv 
iiom 90 : then thefe diftances fuccefiively laid from 
the mark reprefenting 90° at the right-hand end of 
the fcale, will give the feveral divifions of a fcale of lo- 
garithmic fines. 
For, the ends of any fcale being affigned, the pro- 
greffive divifions of that fcale are laid thereon from 
that end, which reprefents the beginning of the pro- 
grefhon : or, the lame divifions may be laid from the 
other end, by taking the complements of the terms 
to the whole length of the fcale : 
Confequently the arithmetical complements of the 
fines are to be laid from the divifion reprefentine oo 
degrees. x 6 y 
To conjiruft the line of logarithmic tangents . 
Thefe are laid down in the fame manner, and for 
the fame reafons, that the fines were; the tangent of 
4f° landing againfl: the fine of 90°. 
The divifions for the tangents above 4^°, are rec- 
koned on the fame line from 45 0 towards the left- 
hand ; or any tangent and its co-tangent are expreffed 
by the fame divifion. ^ 
Thus one mark ferves for 40? and yo°; and the 
divifion at 30° ferves alfo for 6o°; that at 20° ferves 
for 70®, &c. and the like is to be underftood of the 
inte: mediate divifions. 
F01, as the tangent of an arc, is to radius; 
So is radius, to the co-fangent of that arc. 
Therefore the tangent is equal to the fquare of 
radius divided by the co-tangent. 
N 2 
And 
