( 3c8o ) 
foundj which would polifli as finely as Glafs, and reflt^Sl as much 
Ijghtj '^Vd^^ tranfmitSy and the art of communicating to it a Pa- 
rabolicl^ figure be alfo attained. Put there feemed very great dif- 
ficulties, and I have almoft thought them infuperable, wh°n I fur- 
ther confidered^ that every irregularity in a reflecting fuperficies 
makes the rsys ftray 5 or 6 times more out of their due courfe , 
than thclike irregularities in a refracting one : So that a much 
greater curiofuy would be here requifite, than in figuring glades 
for PvefraCtion. 
Amidft thefe thoughts I was forced from Cambridge by the Inter- 
vening Plague^ and it was more then two years^before I proceed- 
ed further. But then having thought on a tender way of politli- 
ing, proper for metall, whereby, as I imagined^ the figure alfo 
would be corrected to the laft s I began to try, what might be cf- 
te^led in this kind^ and by degrees fo far petfecSied an Inftrument 
(in the eflential parts of it like that I fent to London,^ by which I 
could difcern Jupiters 4 Concomitants^ and fliewed them divers 
times to two others of my acquaintance. I could alfo difccrn the 
Moon«like phafe of Venus^ but not very diftinftly, nor without 
lorae nicenefs in difpofing the Inftrument. 
From that time I was interrupted till this laft Autumn, when I 
made the other* And as that was feofibly better then the firft 
(cfpecially for Day-Objedtsjfo I doubt not, but they will be ftili 
brought to a much greater pcrfe(ftion by their endeavours, who, 
as you inform me, are taking care about it at London, 
I have fometimes thought to make ^Microfcope^ which in like 
manner fliould have, inftead of an ObjeCt-glafs , a Reflecting 
piece of metall. And this I hope they will alfo take into confi- 
deration^For thofelnftruments feem as capable of improvement 
as Tele[cops^ and perhaps more, becaufe but one re fleftive piece 
of metali is requifite in thera^as you may perceive by the annexed 
diagram, v^here A B 
reprefentcth the ob- 
jeCt metallic D the 
eye glafs^F their com- 
mon FocuSjand O the 
other focus of the me* 
tall, in whfch the ob- 
jeft iT^placed. 
But 
