( 4035 ) 
be enpeded from thofe of other Lengths by this way, if Art 
can accomplifli what is promifed by the Theory. In the firjl ^ 
Column is exprefled the Length of the Telefcope in feet ^ ' 
which doubled gives the femidiameter of the Sphere^on which 
the concave metall is to be ground. In the fecond colamo arc 
the proportions of the Apertures for thofe feveral Lengths. 
And in the third column are the Proportions of the Charges^ or 
diameter of the fpheres^ on which the convex fupcrficies of 
the eye^glafles are to be ground. 
Lengths, 
Jpertunt. 
Z. 
lOO 
100 
I 
i68 
119 
2 
38; 
141 
B 
383 
«57 
4 
476 
i68 
5 
562 
178 
6 
645 
18S 
8 
800 
200 
lo 
946 
211 
12 
1084 
sat 
i6 
134s 
238 
20 
1591 
aS4 
24 
1S24 
1 »63 
The ufe of this Table will beft appear by example 
Suppofe therefore a half foot Tclekope may diftinftly mag- 
nifie 30 times with aninch Apcrture,and it being required to 
know, what ought to be the analogoas eonftitution and per- 
formance of a four foot Telefcope % By the fecond column ^ 
as looto 47^ § fo are the Apertures, as alio the number of 
times which they magnifie. And confequently fince the half 
foot Tube hath an iQch aperture and magnifieth 30 times ; a 
four foot Tube proportionally fliould have 4,'^ inches aper- 
turt) and magnifie 143 times. And by the third column^ as 
J 00 to 168 3 fo arc their Charges : And therefore if the dia- 
meter of the convexity of theeye^glafs for a half foot Telef- 
cope be I of an inch, that for a four foot fliould be that 
is^ aboutf of aninch^ 
Oooo 2 la 
