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POPULAR SCIENCE REVIEW. 
The above are large amounts, and represent a money value of 
about 6,500,000£., but in addition to sulphur these mines annually 
send 28,000 tons of copper, of the value of 1,680,000^., into the 
markets of the United Kingdom ; this is above nine times the 
amount produced in Cornwall in 1877, and six and a half times 
more than the aggregate production of the United Kingdom 
during the same year. The sulphur supply of France is chiefly 
derived from pyrites mines situated near Lyons, while a large 
proportion of the pyrites consumed in Germany is obtained from 
Westphalia. The pyrites employed in those countries contains 
no copper. 
EXPLANATION OF PLATES III. & IV. 
Plate III. Plan and elevation of an ancient Roman drainage-wheel 
found at the San Domingos Mine, Portugal. This wheel, which is con- 
structed entirely of wood, somewhat resembles an ordinary water-wheel 
in which the buckets have been reversed. As, however, both its internal 
and external rings are continuous, the water, which enters the buckets by the 
apertures in the sides while they are passing through the trough at the 
bottom, can only escape through these same openings when raised to the 
height of the launders, a, and, flowing out on either side, is conveyed to 
another trough, in which is placed a second wheel of similar construction. 
It is evident that by the use of a series of such contrivances, placed one 
above another and all turned at the same time, water can be raised from a 
considerable depth. 
Plate IV. This plate, engraved from a photograph, shows the position 
of the great open cutting at Rio Tinto looking north. The old workings, 
which have been cut into during the progress of the excavation, are partly of 
Roman origin, and in part made by the Spaniards. 
