C 3^50 ) 
1 7. Teaches a new way, of ufing a Telefcope for dTawfng 
in proportion all the new Appearances in the Heavens 5 for 
meafuring the Bodies of the Planets, and of the Fixt Stars 
themfelvcs and their diftances, in fuch parts, thataL^W (the 
twelfth part of ar^ inch) fliall contain a 1000 of themjan inch 
(the twelfth part of a foot) 1200O5 and a foot, 144000.- Be- 
fidesj a very eafie and certain way of ma^king aJI thefe parts 
(though very fmall) perceptible to the bare Eye. 
So far of the fir/l Head of this Third VztU 
The other Head is the Mechanical, fliewing the feveral ways 
of Forming and Polifhing all forts of Glaffes, that ferve for 
Tclefcopes 5 which is done in fixStdAous. 
I. Redifies the Common way of forming GlaflTes Spherically^ 
and all the Moulds, in which the Vulgar Artifts are wont to 
work them. 
Teaches a way of excellently forming and polilhing fuch 
Glafles by hand^without any Engin. 
3. Teaches a way of working Glafles by the hand guided 
by a fimpleEngin. 
4. Treats of the working of Glafles by Inftruments and 
Engins^regulating and direftingthe hand. 
5. Teaches a Newway of working Spherical Concave Eye# 
glafles J to ferve Telefcopes of the firft kind^ above-men- 
tioned. 
6. Teaches a New way of working all forts of Spherical 
Glafles, Convex and Concave, for Teiefcopes^ very univer- 
fally, fpeedily, with eafe, and in a fmall room; even for the 
longefl: Tubes* 
All which the Author concludeth with a Dire<9:ion for a way 
of making Tubes that may ferve to fit up Telefcopical 
Glafles. 
E R R A T 
In?(M«^. 74. p, 1211. i. zj. r. i$ hyXruerut dtfcribiitoMUffet, 
la thiiA«w6. 78. p. soar. \,^^, t,^redi£fed, foi pra^tfed, p. joz^. I. 16. & mttm^ ibid. 1. 
LONDON, 
?nntcd (oT John Mlartf^^ ?nntcv to thQ Royal- Society. v6ju 
