through thisj than through an ordiaary Telefcope of abBUt 
2 foot long. And fo fuppofing this ordinary one to mag^ 
nifie 13 or 14 times 3 as by the defeription k fticuld, this new 
one by the Experiment muft magnifie near as mnch as hath 
beenaflSgned* ^ , ^ 1 r 
Thus far as to the ftrudure of this Telelcope* Concern- 
ing the MetalHne matter, fit for thefe TGAe,£tmg Speculu^f ^ 
the Inventor hath ai(o coofidered the farae, as may be feen 
by two of hisLetters, written to the Pubhflier from Cam- 
bridge Jan. 18. and 29. 16^. to this effe^, vi^. 
u That for a iit metaUine lubftance, he would give this 
Caution, that whileft men feek for a white , hard and du. 
rable metallio compofition, they rcfolve not upon fuch an 
one, as is foil of fmall pores, only difcoverable by a Micro- 
fcope. For though fuch an one may to -appearance take a 
good poliflij yet the edges o{ thofe fmall pores will wear 
away fatter in the poliihing thap the other parts of the me- 
tal- andfo, however the Metailecm poHte, yet it fliall not 
reflea with fuch an accurate regularity as it ought to do. 
Thus Tin-glafs mixt with ordinary Bell-metall makes it more 
white and apt to rcfleft a greater quantity of light j but 
wirhall its fumes, raffed in the fufion, like fo many aerial 
bubles jfill the metall full of thofe Microfcopical pores. But 
white 4rfenick both blanches the Metall and leaves it (olid 
without any fuch pores,efpecialIy if the fuGon hath not been 
too violent. What the Stellate J{egulus of Mars ( which I 
have fometimes ufed) or other fuch like fubftance will do^ 
deferves particular examination. 
To this he adds this further intimation, thsit Putty or©ther 
fuch like powder, with which *tis polifhcd, by the fliarp 
angles of its particles fretteth the metall^if it be not vee 
ry fine, and Ms it f^^ of fuch fmall holes^ as he fpeak- 
eth of. Wherefore care rauft be taken of that, before 
judgraent be given, whether the metall be throughout the 
body of iC porous or mot. 
2. He not having tried, as he faith, many proportions 
of the Arfenick and Metallj does not affirm^ which is ab- 
solutely beft, but thinks^ there may conveniently be ufed 
any 
