( 4^04 ) 
An Accompt ©/ a Nen> Catadioptricul Telefcepe invBtitsd by Mr. 
NewtoD) Fellow of the T^.Society, and frofejjor of the Ma- 
thematiques inthi Vniverji^y of Cambridge. 
THis Excellent Mathematician having given us, in the 
Tf anfadlions of February laft, an account of the caule, 
which induced him to think upon l^fteSing Tclefcopes , in- 
ftead of B^efraUing ones^ hath thereupon prefented the Cu* 
rious World with an E^ay of what may be performed by 
fuch Telefcopes $ by which it is found , that Tclefcopicai 
Tubes may be confiderably ftiortned without prejudice 
to their magnifying effedt. 
This new inftrument is compofed of two Mecallin fiecu* 
lums ^ the one Concave ^ (inftead of an Objedl-gla(s) the 
other Plain 5 and alfo of a fmall plano-convex Eye« 
Glafs. 
By Figure L of Tab, !♦ the flrndurc of if may be ealily 
imagined ; viz. That the Tube of this Telefcope '\& open at 
the end which refped:s the objedt 5 that the other end is clofe, 
where the faid Concave is laid , and that near the open end 
there is a flat oval /peculum^m^de as fmall as may be,the lefs to 
cbfttufit the entrance of the rays of Light, amJincUncd to^ 
wards the upper part of theTiibe, where is a little hole fur- 
nifli't with the faid Eye- glafs. So that the rays coming from 
the objeft, do firft fall on the Coacavc placed at the bot* 
tonieof the Tube j and are thence refle<9:ed toward the o-- 
ther end of ir, where they meet with the flat fpeculumj ob^ 
liquity pofitedj by the refled:ion of which they are direded 
to the little plano-convex Glafs , and fo to the fpe<3:ators 
Eye, who looking downwards fees the Objed, which the 
Telefcope is turned to* 
To underftand this more diflindly and fully, the Reader 
may pleafe to look upon the fsiid Figure, in which 
AB ii the Concave fpeculum^ of which the radius or fcmt- 
diameteris i2f or 13 inches* 
CD another metalline whofe furface is flat, and 
the circumference oval. 
GD 
