f'64 Dr. watson’s Experiments and 
Suppofe that a cubic foot of lead ore, which contained 
no fpar or other extraneous matter, would weigh 7800 
ounces, and that a cubic foot of fpar, which contained no 
laid ore or other foreign fubftance, would weigh 2700 
ounces, then would a mixture, confiding of a cubic foot 
of pure lead ore and a cubic foot of pure fpar, weigh 
10500 ounces, and one cubic foot of fuch a mixture 
would weigh 5250 ounces. It is obvious that, according 
to the different proportions in which the particular kinds 
of fpar and lead ore here aifumed are fuppofed to be 
mixed together, a cubic foot of the mixture will have 
different weights, the limits of which are on the one 
hand 7800, and on the other 27.00 ounces ; it never can 
weigh fo little as 2700 ounces, for then it would confifl 
intirely of fpar without any lead ore; nor can it ever 
weigh fo much as 7800 ounces, for then it would con- 
fifl intirely of lead ore without any fpar. 
From this view of the matter it is evident, that the 
purchafing of lead ore by the meafure, which is the ge- 
neral though not the univerfal cuftom in Derbyfhire, is 
a mode liable to fome exception ; fince a dith, containing 
any definite meafure, muft have different weights, ac- 
cording as the ore with which it is filled is more or lefs 
iree from fpar. And it is fcarce poffible, by repeated 
dreffiifgs., 
