r Sc8s ) 
could be conveniently eShdicd^ there would be no further dif- 
ficulty. Now to this end i examined, what may be done not 
only by Glajps alone, but more efpecialiy by a Complication of 
divers fucceffive M^/^/^/Tj/j as by two or more GlafTes or Cjy» 
ftals with Water or fonie other fluid between them; all wl\ich 
together may perform the office of one Glafs^ efpecially of the 
Objedi-glaff^ on whofeconftrudion the perfediion of tke in- 
ftrument chiefly depends* But what the refults in Theory or 
by Tryals have been, I may polfibly Sod a more proper occa« 
fion to declare. 
To the Affertion, that Rays arc lefs true refleited^to^jpmnt 
by a Concave^ than refracted by a Convex, I cannot affent 5 nor 
do lunderftand^ that the j^^*^ of the latter is lefs a line than 
that of flie former* The truth of the contrary you will rather 
perceiveby this following TablCj computed for fuch a Kefiecm 
ting Concave^ and Refracting convex^ on fuppoficion that they 
have equal Apertures, and colhGt parallel rays at an equal di- 
ftance from their ^'^•r/^:^ • which diftance being divided into 
15000 parts, the Diameter of the Concave Sphere v/ill be 
60000 of thofe parts, and of the Convex, 10000 5 fuppofing 
the«s*/«^/ of Incidence and RefracSbion to be, in round num- 
bers, as 2 to 5* Andthis Table fliews5 how much the exterior 
rays, at feveral Apertures, fall fhort of their principal/irtti". 
The Diameter between the vcrtQK md the rays, 
of the Aperture. Reflected . 1 RefraUed, 
The . 
1 Reflexion. \ 
Error by 
RefraElionl 
2000 
I499if 
14865 
135 . 
4000 
14966 
H449 
33 
551 • 
6000 
14924 
13699 
76 . 
1301 . 
8000 
14865 
12475 
135 
25 -5 ; 
1 0000 
14787 
1 947 2 
213 
1 552« . 
By this you may perceive, that the Errors of the Refracting 
i'ewwArare fo far from being that they are more than fix- 
teen times greater than the like errors of the J^eflectingConcave^ 
efpecially in great Apertures $ and that without refpe<St to the 
Heterogeneous conftitution of light. So that^ however the 
contrary fuppofition might make the Author of thefe Animad* 
verfionsrejed K^^^^^/(?«/as ufelefs for the promoting of Op- 
Kkkkk2 tique^ 
