Tr e atife of the ufefulnefsef great Optic k-Glaffes, where he alfo 'in- 
tends to deliver feveral Experiments, by him made, i . X cach- 
ing the quantity of Light, which a Body, that is io. i$ and 2© 
times, &s. remoter than Saturn] would yet receive from the Sun . 
2. Touching the quantity of Light, by which the Earth is illu- 
minated even in the Eclipfes of the Sun, in proportion of their 
bigtiefs. 3. Touching the quantity of Light, which is neceffa- 
ry to burn Bodies : he having found, that not abating the Light, 
which is reflected by the Surfaces, of the Glafs (whereof he con- 
£efseth,he doth not yet exatXly know the quantity) there would 
be necefsary about y© times as much Light,as we have here, for 
the burning of Black Bodies ; and peer 9 times more for the 
burning of White Bodies, than for the burning of Blacky ones 
and fo obferving the immediateproportions between thefe two, 
for burning Bodies of other Colors. Whence ( he tells us ) he 
hath drawn fome confequences, touching the diftance 5 at which 
we may hope, to burn Bodies here, by the means of great GlaJJes 
and great Looking. glajje s , So that ( faith he ) we muff 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 Infractions to 
certain perfons, gori to travel in Hot Countries , he hath among o- 
ther particulars recommended to them, to try by means of great 
Burning-glajfes , with how much lefs Aperture they will burn there , 
than here, to know from thence, whether there be more Light 
there than here-, and ho w much * fince this perhaps may be the 
only means of trying it,, fuppofing, the fame matters be- 11 fed : al- 
though the difference of the Air already heated, both in hot Coun- 
tries, and in the Planets are neerer than we, may alter, if not 
the quantity of Light, at leaft that of the Heat, found there. 
A further Accounipuching Signor Campani i Book, and Per » 
formances about Optick-glalses. 
In the above-mentioned French Tradfthere is alfo conteined 
M, Au^out's Opinion of what he had found New in the Treatife 
of Signor Campani 5 which was fpoken of in the fi, ft Papers of 
thefe TranfaUions, concerning both the Effecff of the Tele [copes , 
contrived after a peculiar way by the laid Campani at home , and 
