( 400^ ) 
through thisj than through an ordinary Telefcope of about 
2 foot long. And fo fuppoiing this ordinary one to msg? 
nifie 13 or 14 times, as by the deferiprioo it fluuld, this new 
one by the Experiment muft magnifie near as nauch as hath 
beenafligned^ 
Thus far as to the ftruGure of this Telefcope* Concern- 
ing the Metalline matter^ fit for thefe refle<amg Speculutnr ^ 
the Inventor hath alio confidered the fame, as may be fecn 
by two of his Letters^ written to the Publiftier from Cam- 
bridge Jan. 18. and 29. 1677. to this efFe^a, vi^, 
!♦ Tha^tfor a. fit metalline fubftance, he would give thi* 
Caution, that whilefl men feek for a white , hard and du- 
rable metallin compofition , they refolve not upon fuch an 
one, as is full of fmall pores, only difcoverable by a Micro- 
fcope. For though fuch an one may to appearance take a 
good polifhj yet the edges of thofc (mail pores will wear 
away fafter in the poliihing thari the other parts of the me- 
tal • and foj however the Metal (ccm polite, yet it fhall not 
refled: 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 refleft a greater quantity of light 5 but 
withall its fumes, raifed in the fuGon, like fo many aerial 
bubleSjfill the metal! full of thofe Microfcopical pores. But 
white Arfenick both blanches the Metal! and leaves it folid 
without any fuch pores,efpecially if the fufioD hath not been 
too violent. What the Stellate l^egtdus of Man { which I 
have fometimes ufcd) or other fuch like fubftance will do, 
deferves particular examination. 
To this he adds this farther intimation, ih^X Putty or other 
fuch like powder , with which 'tis poliflicd , by the (harp 
angles of its particles fretteth the metall, if it be not ve* 
ry fine, and fills it FuH of fuch fmall holes, as he fpeak- 
eth of. Wherefore care muft be taken of that , before 
judgment be given, whether the mctall be throughout the 
body of it porous or not. 
2. He not having tried, as be faith, many proportions 
of the Arfenick and Metall, does not affirm, which is ab- 
folutely beft, but thinks, there may conveniently be ufed 
any 
