C 3P‘0 
it fomewhat of a Sky-colour, he was , upon owning his furprife 
thereat, informed , that a dozen of them being putin, they 
would dye it to almoft a full Azure, Which is touch’t ’here , 
that, the Experiment being fo eafie- to make, it may be tried, 
when the feafon furniilies thofe Infers 5 mean time, it feemsnot 
more incredible , that this Creature fhould yield a Sky-colour, 
when put in water , than that Gochineel y which alfo is but an 
Jnfeft , fhould afford a fine red, when fteep’d in the fame Liquor. 
An Account 
Of Some Boobj. 
I. Le Tome troifieme et dernier des Lettres de M. DES- 
CARTES, 
As the two firft Tomes of M, Des-Cart es his Letters , contain 
Queftions , for the moft part of a Moral and Phjfi logical Nature^ 
propofed to ? and anfwer d by him 3 fo this confifts of the Con- 
tefts, he had upon feveral Subjects with divers Men eminent in his 
time. 
To pafs by that fharp Conteft, he was engaged in by fome 
Profeffors of Divinity at Utrecht , who endeavoured to difcredit 
his Philo fophy , as leading to Libertinifme and Atheifme , not- 
withftanding he made it fo much his bufinefs , as to affert fhc JEx- 
iftence of a Deity, and the Immortality of a Soul: Weihall 
take notice of what is more to our purpofe , 1 Ad. the Differences, 
he had touching his Dioptricks and Geometrj. 
As for his Dioptricks , though a great part of the Learned 
World have much efteem’d that Tteatife , as leaving little to be 
Did after him upon that Subjedi 3 yet there have not been wanting 
Mathematicians, who have declared their difagreement from his 
Principles in that Dcdtrine. The firft of them was the Jefuit Pour- 
../fcMathematick Profeffor in the Colledg of Clermont at Parity but 
this difference was foon at an end. A fecond was Mr. Hobbs, upon 
whofe account he wrote feveral Letters to Merfnnus , containing 
many remarks conducing to the Knowledge of the Nature of Re- 
flexion and RefraXion, But the Perfon, that did moft learnedly 
and refolutely attack the Laid Dioptricks , was Monfiem Fermat 3 
\ writing 
