And for the Bearing of the l^ng againft one fide of the Glafs 
onlyatatimej I cannot lee, why that ihould produce any ine- 
quality, fince all the fides of the Glafs have fiicceffively the lame 
preffure. 
His ratiocination concerning a Glafs of 300 foot, is much the 
fame with the former , about the diflSculty of working a true 
furface of a convenient figure ; which how confiderable both 
that and his Conclufion thereupon ( mdeL That ive are not to ex- 
pcU Glajps of above 300 or 4C0 foot long at mojl , and that neither 
M^it^v ner kn will go fo far) is, may be judged from what I 
have newly told you of making any objeH* Glafs of any Length. 
And for his good wiflies, that thole, who promife to make 
him itt P lants QvAnmals in xh^ Moon (of which I know not 
any, that has donelo, though perhaps there may be fome, not- 
Withftandinghis Objedions, that do not yet think it impofliblc 
to be done) had confidered, what a Man is able to fee with his 
hare Eye at 60 Leagues diftance : I cannot but return him my 
wiilies, 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 tlori^on, and neer the Zenith with a TekfcopCy he will ex- 
perimentally find ; and, having done fo, he will perhaps not be 
10 diffident in this matter* 
Concerning his Advertifementtofuch, as publifli Theories ^ 
I find not, that he hath made ufe of it in his own cafe. For, in 
his Theory about ^/^^r/^r^/ he feems to be very pofitive, not at 
all doubting to rely upon it, vid, that the Apertures muft be thus 
and thus iugreat GlafleSj becaufe he had found them fo or fo in 
fome fmali ones. 
For his Propofal of 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 eoncaveTool^as on the 
convex Glafs. And as to that of 2 Poppet.be ads, \ do not well un- 
derftand !t,if differing from mines and the keeping of the Tool 
upon the Glals with a fpring or weight, muft quickly Ipoyl 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 
