-'^r. Ifaac New ton V Confi derations upon part of a Letter of 
Monfieur de Berce printed zn the Eighi French Memoire, con- 
cemino the Cata dnoptrical Telejcope^pretendedto be improv'd 
and refined by M. Cairegrain. 
That the Reader may be enabled the better to "judge of the rvhole 
by comparing together the contrivances both of Mr^ Newton /3«^ 
Mr. Caffegrain 5 it will be nece£ary , to borrorv from the [aid 
French Memoire what is there faid conctrningthtm : which is as 
foil owes, 
I Send you, ( faith M. de Bsrce to the Publiflier of the n^fe* 
moire^ ) the Copy of the Letter, which M. Caffagrainhdnh 
written to me concerning the proportions of Sr» Samuel 
2V/(?r^/^W/ Trumpet. And as for the Telefcope of Mr. JSIen>^ 
/cwit hath as much furprifed me^ as the fame Perfon, that 
hath found out the proportions of the Trumpet, For*tisnow 
abbut three raonths^that that perfon communicated to me the 
figureof a Telefcope, which was almoft hkeit^ and which he 
had invented; bat which I look upon as more witty* I fliall 
here give you the defcription of it in fhort» 
ABCD. is a ftrong Tube, in the bottom of which there 
is a great concave Speculum CD, pierced in the midle E. 
F\» is a convex Sptcu'um^ fo difpofed , as to its convexity , 
that it reflects the Species^ which it receives from the great Spe^ 
culuwy towards the hole where is an Eye-glafi, which one 
looketh through. 
The advantage, which I find in this Inftrument above that 
of Mr- Newton^ is firft , that the mouth or aperture AB of the 
Tube may be of whatbignefs you pleafe » and confequently 
yon may have many more rays upon the Concave Speculum^ 
than upon that , of which you have given us the defcription. 
1. The reflexion of the rays will be very natural^ finceitwill 
6e made upon the axis it felf ^ and therefore more vivid. 
3. The vifionof it will be fo much the morepleafing, in that 
you fliall not be incommoded by the great light^ by reafon of 
ih^: bottom CD^ which hideth the whole face^ Be/ides that 
you1 
