( 4007 ) 
any quantity of Arfenick equalling in weight between a fixt 
and eight part of the Copper^ a greater proportion making 
the Metal brittle* 
The way, which he ufed, was this. He firft melted the 
Copper alone, then put in the Arfenick, which being melted, 
he ftirred them a little togctherjbewaring in the mean titae., 
not to draw in breath near the pernicious fumes* After this^ 
he put in Tin^ and again fo fooo as that was melted ( which 
was very fuddenly) he ftirred them well together , and im- 
mediately powred them ofF^ 
Me faith y he knows not^ whether by letting them ftand 
longer on the fire after the Tin was melted, a higher degree 
of tufion would have made the metall porous i but he thought 
that way he proceeded to be fafefl. 
Be add that in that metail, which he fent to Zo;2^o«,thcre 
was no Arfenick, but a fmall proportion of Silver • as he re- 
members^one Ihilling in three ounces of metall.But he thought 
withall, that the Silver did as much harm in making the me^ 
tail foft, and fo lefs fit to bepolifh't, as good in rendring it 
white and luminous* 
At another time he mixed Arfenick one ounce. Copper fix 
ounces.and Tin two ounces : And this an Acquaintance of his 
hath,ashe intimatesjpolifli't better,than he did the other. 
As to the objeUion^ that with this kind of Perfpedlives, ob* 
jedls are difficultly found, he anfwers in another letter of his 
to the Ppbliflier, of Jan. 6. i6^. that that is the inconveni- 
ence of^ all Tubes that magnifie much % and that after a little 
ufc the inconvenience will grow lefs, feeing that himfelf could 
rea4ily enough find any day-Objeds, by knowing which way 
they were poficed from other objedls that he accidentally faw 
in it ; but in the night to find Stars , heacknowledges it to be 
more troublefome 5 which yet may, in his opinion, be eafily 
remedied by two fights affixed to the Iron rod, by which the 
Tube is fufteined 5 or by an ordinary perfped:ive glafs fafln'd 
to the fame frame with the Tube^ and directed towards the 
fatae objed:, as Des- Cartes in his Dioptricks hath defcri- 
bed for remedying the fame inconvenience of his beft Te- 
Icfcopeio 
L 11 1 S9 
