(W) 
And for the Bearing of the Rjng againft one fide of the Glafs 
only at a time., I cannot fee , why that fhould produce any ine- 
quality, fmce all the fides of the Glafs have fucceffively the fame 
prefilire. 
His ratiocination concerning a Glafs of 3C0 foot, is much the 
fame with the former, about the difficulty of working a true 
furface of a convenient figure; which how confiderable both 
that and his Conclufion thereupon ( videl. That ne are not ta ex- 
peH Glajfps of above 300 or 400 foot long at * mofl , and that neither 
Matter nor Art will go fo far ) is, may be judged from what I 
have newly toldyou of making any ohjeU-Glafs of any Length. 
And for his good wilhes, that thole, who promife to make 
him fee Plants or Animals in the Moon ( of which I know not 
any, that has done fo, though perhaps there may be fome, not- 
withftandinghis Objections, that do not yet think it impoffible 
to be done) had confidered, what a Man is able to fee with his 
Eye at 60 Leagues diftance: I cannot but return him my 
willies, that he would confider the difference between feeing a 
thing through the Grofs and Vaporous Air neer the Earth, and 
through the Air over our heads ; Which, if he obferve theMoon 
in the Horizon, and neer the J^enitb with a Telefcope , he will ex- 
perimentally find ; and, having done fo, he will perhaps not be 
fo diffident in this matter. 
Concerning his Advertifementtofuch, as publilh Theories s 
I find not, that he hath made ufe of it in his own cafe. For, in 
his Theory about Apertures he feems to be very pofitive, not at 
all doubting to rely upon it, vid. that the Apertures muff: be thus 
and thus in great Glafles,becaufehe had found them fo or fo in 
{omc final l ones. 
For his Propofalof amendments of fome inconvenieneies in 
this way, I return him my thanks ; but as to his firft I believe, that 
the matter may be conteined as wel in the Concave Tool,as on the 
convex Glafs. And as to that of 2 Poppet-heads, Ido not well un- 
derftand it, if differing from mines and the keeping of the Tool 
upon the Glafs with a fpring or weight, muff: quickly fpoyl the 
whole ; fince, if either of the Mandrils will eafily yield back- 
wards, the regularity of all will be fpoiled : and as to the wrigling 
and playing of the Mandril , I do not at all apprehend it. 
His 
