His Theory of Apertures, though he feems to think it very an- 
thentick, yet to me it feems not fo cleer. Forj the fame Glafs 
will endure greater or leffer^/^^r/ajr^/, according to the leffer 
or greater Light of the ObjeU : If it be for the looking on the 
Sm or F'enuf, or for feeing the Diameters of the Fix'd Stars^thtB 
fmaller Apertures do better j if for the Moon in the daylight^ or oa 
Saturn.or Jupiter^ or Mars, then the largeft. Thus I have often 
madeufe of a 12 foot- Glafs to look 00 Saturn with zn Aperture 
of almoft 5 incheSj and with a fingle Eye-glafs of 2 inches do?i^ 
hie convex \ but, when with the fame Giafs I looked on the 
Sunoi Venus ^ I ufed both a fmalkr Aperture, and fhallower 
Charge, kvidi though M. Au^out feems to find fault with the En^ 
gUfljGhi% 16 footjthathad auv^/^r/^rf of but 2\ inch^sFrench; 
as alfoj with a foot TuhjUkd but with an Aperture of 3 inch- 
es; yet I do not find^that he hath feen Glaffes of that lengtli^chat 
would bear greater ^^^r^g^w 5 and 'tis not impoffible 3 but his 
T^^orj of y^j^^r/#^j" may fail in longer GtalTes. 
Of a meam to iUuminate an ObjeB in what fro- 
portion onefleafeth ; and of the Diftances re- 
quifite to burn Bodies by the Sun. 
One of the means ufe^l by M. Au^ut to enlighten an Objedl, 
in what proportion one pleafeth^ is by fome great ObjeU-Glafs , 
by him called a Planetary one, becaufe that by it he fhews the 
difference of Light, which all the Planets receive from the Sun^ 
by making ufe offeveral .^//5r^2^w, proportionate to their di- 
ftance from the Sun, provided that for every 9 foot draught or 
thereabout, one inch of Aperture be given for the Earth. Doing 
this, one fees {faith he ) that the Light which Mercury receives, 
is far enough from being able to burn Bodies, and yet that the 
fame Light is great enough in Saturn to fee cleer there , feeing 
that (to him) it appears greater in Saturn, than it doth upon our 
Earth, when it is overcaft with Clouds : Which (he adds) would 
fcarce be believed, if by means of this Glafs it did not fenfibly 
appear fo; Whereofhe promifes to difcourfe more fully in his 
K Treatife 
