(5P5) 
writing firft about it to Merfenms , who foon communicated his 
Objeftions toM. Des-Canes^ who failed not to return his Anfwer 
to them. But Fermat replied, and Des-Cartes likewife 5 and after 
many reciprocations, in which each party pretended to have the 
advantage, the matter refted; until M. F^m^^ taking occafion to 
write afrefh of it to M. De laChambre ^ feveral years after D^i- 
€artes\ death > upon occafion of a Book , written by M. BeU 
Chambre^ of Light difcourfed with this new ^^^^i?r after the 
fame rate 3 as he had done before with Bes-Cartes ^ and 
feemed to invite fome-body of his friends , to re-aflume the for- 
mer conteft. Whereupon M, Clerfelier and M. Rohadt took up 
the Gantlet , to alTert. the Dodlrine of the deceafed Philofopher^ 
exchanging feveral Letters with M. Fermat^ all inferted in this 
T erne , and ferving fully to inftrud the Reader of this Difference^ 
and withal to elucidate many difficult points of theSubjedlof Re- 
fractions efpecially of this p^cular ^ Whether the Motion of 
Light is more eaftlj and wit^ more t>cf edition ^ f erf ornid through 
dth^Q Mediums , t han rare, / 
Eefides this , though ode would think 5 Difputes had no place 
in Geometry J fince all proofs there , are as many Demonftrations; 
yet M.Des'Carres hath had feveral fcufles touching that Science, 
As M. i^(fm^^had afTauked his Biof tricks^ fo He reciprocally ex- 
amined Be Maximis & Minimis ^ pretending to have 
met with Paralogifmes in it. But the Caufe of M. Fermat was 
learnedly pleaded for 5 by fome of his Friends , who took their 
turn to examine the Treatife of Bes-Cartes's Geometry^ where- 
upon many Letters were exchanged, to be found in this Book, 
and defer ving to be confidered 5 which doubtlefs the Curious 
would eafily be induced to do 5 if Copies of this Book were to be 
obtain'd here in 5 befides that one, which the" P/^^///??^r 
received from his Pariftan Correfpondent ^ and which affords him 
the opportunity of giving this, thoitgh but Curfory, Account 
of it. 
As to Phjficks^ there occur chiefly two Queftions, learnedly 
treated of in this Volume , though not without fome heat between 
M. Bes-Cartes mdM. Moherval. The of^e is touching the Vi- ,. 
brations of Bodies fufpended in the Air , and their Center oi^ 
Agitation : about which , there is alfo a Letter inferred of 
V f f ISlPcs-^Cartcs 
