' Ifaac^NewtonV Conf derations upon part of a Letter of 
Monfieur de Berce pnntedin the Eight French Mcmow^^ con, 
cefPMi2^the Cata drwptrtcal Telejcope^prethidedto be 
^ - J^i andj^^edh M^C^ikgrzw. 
That the Reader may be enabled the better to Judge of the rvhsk^ 
by comparing together the contrivances both of Mr ^ Newton ^/a^ 
Mr„ Caffegrain • it will be necepry , to borrow from the [aid 
french Memoir c what is there /aid concerning them : winch is 
foil owes, ^ 
ISeod you ( faith de Berce to the Pubh'flier of the 4^ 
moire ^ ) the Copy of the Letter, which M. Caffagrain hath 
written to me coacerning the proportions of Sr» Samuel 
M or eland sTxmn\)m Andasfbr the Telefcope of Mr. TSlew. 
lo^ithath as much furprifed mCj as the fame PerfoOj that 
hath found out the proportions of the Trumpet. For 'tis now 
sbout three months^that that perfon communicated to me the 
figure of a Telefcope, whxh was ahuoft hke it^ and which he 
h^d invented j but which I look upon as more witty* I fliall 
here give you the defcription of it in fliort. 
AbCD. is a ftrong Tube, in the bottom of which there 
is a great concave Sf eculum CO^ pierced in the midle E. 
is a convex Specu^um^ fo difpofed ^ as to its convexity , 
that it reflcdls the Species^ which it receives from the great spe'* 
culumy towards the hole where is an Eye-glafs^ which one 
looketh through. 
The advaorage, which I find in this Inftrumeot above that 
of Mr- i\fe?p/^f?3 isfirft, that the mouth or aperture AB of the 
Tube may be of what bignefs you pleafe; and confequently 
5^QU may have many mor@ rays upon the Concave Speculum^ 
khm upon that , of which you have given us the defcriptiou. 
1. The reflexion of the rays will be very natural/ finqe it will 
6e made upon the c^xis it felf ^ and therefore more vivid. 
3. The vifioo of it will be fo much the more pleafing, in that 
you fhall not be incommoded by the great lightj by reafon of 
the bottom CD^ which hideth the whole facevBefides thac 
youl 
