inftrument will be but fmall^the object dark aed confufed^and 
alfo difficult to be found. Nor do I fee^ why the reiflexion is 
mors upoq the fyme accu^and fo raore natural in one cafe than 
in the other : fince the axis it felf is tefleded towards the Eye 
by the Oval plains ' and the Eye may be defended from ex- 
ternal light as well at the fide, as at the bottome oftheTube^ 
You (ee therefore, that the advantages of this defign are 
none, but the dilad vantages fo great arid uoavoidable, th^t ^ 
fear it willneyer be put in pradlile with good efFe<9:* And when 
Iconfider, that by reafonof its refemblance with other Te* 
Icfcopes it is {omcthing more obvious than the other conftruft* 
ion ; l^m apt to believe, that rhofe^who have attempted any 
thing ih CacoptrickSj have ever trycd it in thefirft placejand 
that their bad luccefs in that attempt hath been the caufe, why 
nothing hath been done in reflexion?. For^Mr. Gre^^^ry, fpeak- 
ing of thefe inftruments in the afarefaid book pag 9 f 5 fayethi 
Demechanica horum \pechlornm & leniium ^ab aliis ftujlra ienta^ 
ta^ $go in mechanicis minus verfatm nihil di(o. So that there have 
been tryals made of thefe Telefcopes^ ^^ut yet in vain* Aud I 
am informedjthat about 7 or S years ^tiC^^Mw Gregory himfelf, 
at Londert^ caufed one of fix foot t^ be made by Mr» J{eive^ 
which I take to have been accordiiig to the aforefaid defign 
defcribedin his book 5 becaufe^ though made by a skilful Ar- 
tiftj yet it was without fuccefs. 
I could wifli therefore , Mr* Cafffgrain had tryed h'$ defign 
before he divulged it But if/or further fatisfadion^ he pleafe 
hereafter to try it, I believe the fuccefs will inform him, thast 
fuch prbjeds are oflittle moment till they be put pracSife^ 
Some Experiments prepf/d m rehtim u Mr, Ncwtom Theorj of 
iigkh f™i^d tn Numb, 80 ^ together mith the Obfervatum made 
thereupon by the Author of that Theory j esrnmmmatid m 
Letter of iis Jr orn Cm\bT\d^^ 
I. >-^0 coBtraa: the beams of the Son without the- h^Ieof 
J_ the window 3 and to place the prifm betwean the 
focus ofthe Lms and the ho!e/poken of in M.Nemons theorf 
of lighr^ 
