(7o) 
Treatifeof the ufefulnefssf great Optic\'GUjfes^ where he alfo in- 
tends CO deliver feveral Experiments, by him made, i . Touch- 
ing the quantity of Light, which a Body, that is lo, 15 and 20 
times, ^e. remoter than iS^^z^r/i, would yet receive from the Sun, 
2. Touchingthequantity of Light, by which the Earth is illu- 
minated even in the Eclipfes of ih^Stm, in proportion of their 
bignefs. 3. Touching the quantity of Light, which is ncceffa- 
ry CO burn Bodies : he having found, that not abating the Light, 
which is reflected by the Surfaces of the Glafs (whereof he con- 
fefsethjie doth not yet exa(9:ly know the quantity; there would 
be necefsary about 5-0 times as much Light, as we have here, for 
the burning o^Blask Bodies ; and neer 9. times more for the 
burning of ^kite Bodies, than for the burning of Bla^k.^ ones: 
and fo obferving the iii\mediateproportions between thefe two, 
for burning Bodies of Colors. Whence (he tells us) be 
bath, drawn fome confequences, touching the diftance^at which 
we may hope, to burn Bodies here3 by the means great Glajjes 
iind great Looking. glaffis. So that ( faith he) we muft yet be feven 
times neerer the Sun^ than we are, to be in danger of being bur- 
ned by it. Where he mentions, that having given InJiruBtons to 
certain perfons, gon to travel in hi^t Comtrtes, he hath among o- 
ther particulars recommended to them, to try by means of great 
Burning'glaJJef ^mlh how much lefs Jperture they will burn therey 
ihikwhre, to know from thence, whether there be more Light 
ihsre than here\ and how much ; fince this perhaps may be the 
only means of trying it, fuppofing, the fame matters be ufed : al- 
though the difference of the Air already heated^both in hotCoun*^ 
/w/,an<l in the ?/^^^^/,that are neerec than we^may alter,if Dot 
tJie quantity of Light,at leaft that of the Heat,found there* 
A further AccounUtouchwgStgriorCzmpzms BooKand Pef^ 
formances about Optick-glafscs. 
In the above-mentioned Fr^;2^^6 Trad:, there i§ alfo conteined 
M. Au:{out's Opinion of what he had found Ne w in the Treatife 
of Signor Campani^ which was fpoken of in the firft Papers of 
thefeTr^w/^^i<?«/,concerning both the Effcitof the Telefcopes^ 
contriv ed after a peculiar way by the faid Campani git Komej and 
