An InfimAtkn given inthe Journal dcs Scavans,^/ a Jure and 
ea/te way to make aH forts of great Telefcopfcal Glaffes^ 
together with a generotu offer of furni^ing tniufiriem A- 
(tronomers with them. 
THe llfefulnefs of great Glafles for Telefcopes ^ and the 
care and pains hitherto taken to perfeft this Invention 
isfufficienrly known; but thedifficulty of the work doth io 
ranch increafe in great Glaffes of that kind , that it hath noc 
been furoiounted hitherto. 
Monfieur Borelli, one of the Royal Academy of the Sciences 
of Parts, whofe addition to Natural Philofophy, and chiefly 
to Chymiftry ,hath been known long fince,hath found out a fure 
and very eafie method to work all forts of fuch great Glafles, 
which hath never failed him. He hath already carried the Ex- 
perience of his Secret to extraordinary bigneffes, having made 
one of them very good of two hundred foot, wrought on both 
fides on the fame rule : Which fiiews , that if he had wrought 
it flatonboth fid^^ the glafs would have been of four hundred 
foot. 
This eafinefs of making great Glaffes, and the defire of pro- 
curing fome advancement to Aftronomical difcoveries, have in- 
duced him to make prefents of them in divers places to fevera! 
perfons capable to make ufeof them ; And the fame motive 
doth now invite him to make the like offer not only to the A- 
ftronomers that are difperfed up and down in the Kingdom of 
France^ but alfo to thofe that are in forreign Countries ^ efpe^^ 
cially in thofe parts^ where there is fome eftablifted Academy 
or Society for Aftronomical Obfcrvations i ofFering in thi^ 
cafe to every one of fuch Societies three very good Glafles ^ 
one of tenor twelve foot for a Chamber; another of twenty 
five or thirty foot for ordinary obfervations , and a third of 
fixty or eighty foot,fomake new difcioveries with. 
Private perfons that are not in a condition to make Engins 
for great Glafles, may, at Jeaft, make ufe of Glafles of fourteen 
or twenty foot, which he is willing to fend them, therewith re- 
gularly to obferve the Eclipfes of the Satellites of J^tpster 
which happen almqft every day'^ and afford fo fair a way for 
eftablifliing 
