writing firft about it to "Mer f earns * wfio foon communicated his 
Objections toM. Bes-Cartes, who failed not to return his Anfwer 
to them. But Fermat replied, and Bes-Cartes likewife* and after 
many reciprocations, ■ in which each party pretended to have the 
advantage, the matter refted 5 until M. Fermat t aking occafion to 
write afrefh of it to M. BelaChambre ', feveral years aft$r Des- 
cartes's death, upon occafion of a Book , written by M. Bela 
Chamhre , of Light*, difcourfed with this new Author after the 
fame rate, as he had done before with Bes-Cartes himfelf , and 
feemed to invite fome-body of his friends , tore-afiume the for- 
mer conteft. Whereupon M. Clerfelier and M. Rohault took up 
the Gantlet , to aflert the Dodrine of the deceafed Philofopher, 
exchanging feveral Letters with M. Fermat , all infer ted in this 
T eme , and ferving fully to inftruCl: the Reader of this Difference,, 
and withal to elucidate many difficult points of theSubje&of Re- 
fractions * efpecially of this particular , Whether the Motion of 
Light is more eafily , and with more exp edition perform d through 
denfe Mediums , than rare. 
• Befides this , though onpwould think , Difputes had no place 
in Geometry , fince all proofs there , areas many Demonftrations; 
yet M .Bes-Cartes hath had feveral fcufles touching that Science. 
As M. Fermat had aflaulted his Bioftricks , fo He reciprocally ex- 
amined his Treatife Be Maximis dr Minimis , pretending to have 
met with Paralogifmes in it. But the Caufe of M. Fermat was 
learnedly pleaded for, by fome of his Friends , who took their 
turn to examine the Treatife of Bes-Cartes\ Geometry 3 where- 
upon many Letters were exchanged , to be found in this Book, 
and deferving to be confidered 3 which doubtlefs the Curious 
would eafily be induced to do , if Copies of this Book were to be 
obtain’d here in England, befides that one, which the Puhlijher 
received from his Pari fan Correfpondent , and which affords him 
the opportunity of giving this , though but Curfory, Account 
of it. 
As to Phyfeks, there occur chiefly two Queffions, learnedly 
treated of inthis Volume , though not without fome heat between 
M. Bes-Cartes and M. Rohevval, The one is ^ touching the Vi- 
brations of Bodies fufpended in the Air , and their Center of 
Agitation : about which , there is alfo a Letter inferred of 
F f £ M,J)is- Cartes 
