866 Dr. watson’s Experiments and 
They were employed this year at Holywell in fmelt- 
ing a lead ore from the Ifle of Man ; the ore was rich in 
filver. A lum,u of this ore, weighing about ten ounces, 
was broken into feveral pieces, and fuch of the pieces 
were feleited as appeared to the eye to be wholly pure. 
By taking the fpecific gravities of fix of thefe pieces I 
found, that a cubic foot of the lighted; kind would have 
weighed 6565 ounces, and a cubic foot of the heavieft 
kind would have weighed 7636 ounces. Suppofing the 
fpecific gravity of water to be denoted by 1,000, the 
mean fpecific gravity of the fix different pieces of this 
ore may be expreffed by 7 . 1 1 5 . 
A very pure fpecimen of teffellated lead ore, from a 
mine near Afhover in Derbyfhire, was broken into fix 
pieces, weighing near one ounce each. A cubic foot of 
the lighted: of thefe pieces would have weighed 7 3 26 
ounces, and a cubic foot of the heavieft would have 
weighed 7786 ounces. The mean fpecific gravity of the 
fix pieces was 7.566. 
At the fame mine they frequently meet with fmall 
quantities of fteel-grained lead ore. Six different pieces 
of the fame lump of this kind of ore were chofen, each 
of which appeared quite free from fpar and every other 
impurity. A cubic foot of the lighted: of thefe pieces 
would have weighed 7188 ounces, and a cubic, foot of 
a the.; 
