( 403? ) 
be eupefted from thofe of other Lengths by this way, if Art 
can accomplifli what is prpraifed by the Theory, In thtfirfi 
Column is exprefied the Length of the Telefcope in feet 5 
which doubled gives the femidiameter of the Sphere^on which 
the concave mecall is to be ground. In the fecond column are 
the proportions of the Apertures for thofe feveral Lengths. 
And in the third colxxmn 2lxc the Proportions of thc Charges^ot 
diameter of the fpheres, on which the convex ftiperficies of 
the eye^glaffcs are to be ground. 
Lengths, 
H 
1 
2 
3 
4 
5 
6 
8 
10 
12 
16 
20 
24 
1 
Apertures. 
100 
168 
476 
562 
645 
800 
946 
1084 
»345 
1591 
1824 
1 
Char^ej. 
119 
141 
157 
168 
178 
186 
200. 
211 
221 
238 
*S4 
263' 
The ufe of this Table will beft appear by example 
Suppofe therefore a half foot Telefcope may diftin^tly mag- 
nifie 30 times with an inch Apcrture,and it being required to 
know, what ought to be the analogous conftitution and per- 
formance of a four foot Telefcope : By the fecond column 3 
as 100 to 47^5 fo are the Apertures, as alio the number of 
times which they magnifie. And confeguently fince the half 
foot Tube hath an iach aperture and magoifieth 310 times ; a 
four foot Tube proportionally fliould have 4;^^ inches apeir« 
ture^ and magnifie 145 times. And by the third column, as 
loo to 168 5 fo are their Charges 1 And therefore if the dia- 
meter of the convexity of theeye^glafs for a half foot Telef- 
cope be 1 of an inch, that for a four foot fliould be that 
i$3 aboutf ofaninch* 
Oooo 2 III 
