(6i) 
fee the Moon^ but as if we were a i ©o, or at leaft, 60 . leagues df* 
*ftant from her without a Glafs. He here wiihes, that thofe , 
that promife to make us fee Animals and Plants in the Moon , 
had thought on what our naked Eyes can make us difcern of 
fuch Objects, only at io or 12 leagues diftancc. 
But this he would not haveunderftood as a difcouragement 
from fearching with all care and earneftnefs after the means of 
making long Telefcopes, or of facilitating the working thereof ; 
but only as an Advertifement to thole, who light upon the The- 
ory of any Engine , not to expofe it prefently as poffible and ufe- 
ful, before they have tried it 5 or if it have fucceeded in fmall 5 
iriot to endeavour to perluade, that it will alio fucceed in great. 
As it may happen ( faith he ) that the Engin of Mr. Hooj^ may , 
by tiling ail neceffary precautions/ucceed in the makingof Eye- 
GlaJJes^OY Jmatt Optick-GlalTes, but not in making great ones ; 
as we fee, that an inftrument compofed of two Rulers, where- 
with are traced Portions of Circles , fucceeds well enough in 
when there is no more than half a Line, a quarter of a 
Line, or lefs convexity,it will be no longer juft at all,as he tells 
us to have made the proof of it inCircles drawn by the means of 
one of thefe Inftruments, made by one of the beft Workmen 
in his time, who, whilft he lived, efteemed them above price, 
although they be not juft 5 as others and my felf ( faith he ) have 
bytrya! found, when we endeavoured to make Moulds by their 
means, & as thofe,who by the like Inftrument laboured to trace 
portions of Circles of 80 or 100 foot, &e. Diameter , can atteft. 
But, notwithftanding all this, he hath thought upon two or 
three things, which he thinks may remedy fome inconvenient 
cies of Mr. Ho^his Turn . The firfi is, to invert the Glafs, and 
to put it under the 7 ^f«g,that fo not only the Glafs may be placed 
more Horizontally > and not Hide upon xh^Cement.buX. that the Sand 
alfo,and the Putty may ftay upon the Glafs. 
The other is, that there muft be two Poppetheaels^ into which 
the Mandril muft pafs, where the "Ring is to be faftned 3 and the 
'Mandril muft be perfectly Cylindrical , that fo it may advance 
upon the Glafs as it wears away by the means of its weight, or 
by the means of a fpring, prefling it, without wrigling from one 
place to another, as it would prefently happen in the falhion , 
I as 
