r 83 1 
The Glajjes ufed to mak^ thefePifcoveries. 
The Diftance of theie two V I a^et Sy-whidi 1$ almofl: Infinite 
in refpe£t of their Magnitude, Bad kept^^ t^ much 
longer concealed, ifwehad not for-this purpdfe m ule 
of Glaffes of extraordinary Force. They were firli of all 
feen m March Anno 1684, by two excellent Objefl: Glaffes 
of 100 and 136 feety and afterwards by two others of 90 
and TO feet J all made by Sigr. Campam and lent from Rome 
to the Royal Obfervatory by the Kings order, after the dif= 
covery of the third and fift Satellites^ which had been made 
by others of his Glaffes of 47 and ^^feet. We made ule of 
them without Tubes^ by amorefimple contrivance than 
thole propofed either before or fince. We have fince ieen all 
th^ik Satellites with that of 3:4 feetj and contitiwed to ob« 
ferve them with Glaffes of Mr. Borelli of 40 and yo/e-^f, and 
by thofe which Mr. -^r^^?/^^'/^^/ hath lately made, of 80, 155 
and 220 feet. It was eafy for us to fee theie two Satellites 
by theie different forts of Glaffes, after having found the 
Rules of their Motion, whereby we might with more par- 
- ticular attention look upon the places where they ought to 
be. 
We placed theie great Glaffes fbmetimes upon theObler* 
vatory, fometimes^pon great Mafts, iometimes upon the 
Tower of Wood^ which his Majefty has caufed to be 
brought for this purpoie from ik&r/)', upon the Terrais of 
the Obiervatory. Laftly we put tliem in a Tube raifed up- 
on a fupport made like a Ladder with three leggs, which 
had all the fucceis we defired. 
After having diftinguifhed theie 2 S^^^ii(^>^j from the fixt 
Starrs, from the other S^^^///>^j of S^//^r;?, and from each 0» 
ther, and found the periods of their Motion, we have efta- 
bliihed Epochs from Obiervations, as near as we could to 
the Conjunctions. 
