(125) 
fliould be of tbe diftance given ^ having the Focus of 
the objelt-gkff given equal to and the diftance 
given to BtDfs the diftaace between the firft and the 
fecond Glafs will be equal to '"^^^^^^ whence fubdiiding B 
(the Focus of the ohje^-glafs given) there remains . 
and if this fum be fuppofed equal to we fliall eafily 
knowjby the precedent Rule ,the Fecus of the / ecoi^d Glafs. 
So far M. AuzQut^ who^ I truftj will receive due fatisfa - 
ftion to his defire, as foon as the happy end of the prefent 
Contagion (hall give a beginning and life again to the Studies 
and Anions of our retired Vhilofophers. 
I fliall onely here adde^ That the Secret he mentions \of 
meAfurmg the diftance of Places a Telefcope (fitted for that 
furpofe) and from onejldtion} is a thing already known (if 
I ara not mif-informed) to fome Members of our Society 5 
who have been a good while fince conGdering of it^ and 
have contrived ways for the doing of it : Whether the fame 
with thofe of Mr. Anzout^ I fenuw aor. Nor have I (at the 
diftance that I am now from them^ opportunity of particu- 
lar Information. 
An Experiment of a way of preparing a Liquor that 
Jhall ftn\ into-, and colour the whole Body of Mar- 
ble, cauftng a PiQiure, drawn on a furface^ to 
appear slfo in the inmoik parts of the Stone. 
This Experiment^ having been hinted at in the next fore-- 
going Papers-y out of the Mundus Subterraneuf of Atham^m 
lOrcher^ and feveral Curious Pcrfons, who either have not 
the leifure to read Voluminous Authors^ or are not readily 
skilled in that Learned Tongue wherein the faid Book is 
written, being very defirous to have it transferred hither^, 
it was thought fit to comply with their defire herein. 
The Author therefore of the Mundns^ &:c3 having feen • 
fome 
