of Springs, and llieir Intensity at various Periods of the Year. 1 73 



rain-water carried off by the adit, counterbalanced by the de- 

 ficiency of the engine's actual performance, when compared 

 with its calculated duty. In which case the preceding numbers 

 would nearly represent the intensities at that spot, provided 

 we could apply a correction for the increase due to the hori- 

 zontal increase in the extent of the mine. But the whole of 

 this water is not drawn from the bottom, for in most of the gal- 

 leries ("levels") there is some which is conveyed to the en- 

 gine without being permitted to descend ; yet as the veins are 

 usually very porous, the greater part (say four-fifths) comes 

 to the bottom, and the larger portion of the remainder from 

 but little above; this obtains, however the depth may be aug- 

 mented. The columns in Table II. are independent of one 

 another; the lowest number in each being unity, they exhibit 

 the monthly intensity of the springs in the various mines, on 

 a mean of seven years ; the column " ratio" denotes the relation 

 of the average number of strokes per minute made by all the 

 engines in Cornwall, and " rain," the ratio of rain ; both for the 

 same period. I purposely select mines in various parts of the 

 county, the most distant being about thirty-three miles apart. 



Perhaps it may be expected that I should offer some expla- 

 nation of the differences in the following columns ; but were 

 I to attempt it, it must after all be very hypothetical. I there- 

 fore decline affording any. 



It may not be out of place to observe, that when the United 

 Mines were worked to a depth of 208 fathoms, the mean 

 monthly quantity of water drawn out was about 13,000,000 

 cubic feet ; at present they are worked to 90 fathoms depth, 

 and the mean may now be about 4,350,000 cubic feet. 



The area of the portion ofGwenap parish, which would be 

 included by a line drawn in an east-north-east direction from 

 Pennance to Huel Friendship, thence west -north -west to 

 Huel Derrick, and from there south to Pennance, is about 

 1969 acres. Within this line are all the mines mentioned in 

 Table III., there being steam-engines worked on them ; be- 

 side others on which there are no engines, they being drained 

 by the adjacent mines. Within the bounding line there are 

 not more than three or four wells, but along the south and 

 west lines there are several at a little distance ; whilst about 

 a quarter of a mile north of the north line is the stopped mine 

 of Huel Busy, in which the water is at the adit This affords 

 a tolerably favourable opportunity for comparing the quantity 

 of rain, falling on a known area, with the evaporation, and 

 the quantity of water afforded by springs in a given time, from 

 the same spot. The following columns, Table III., contain 

 such a comparison ; the evaporation being estimated from the 

 register of W. Snow Harris, Esq. of Plymouth, who kindly 

 permits me to'use his numbers ; and the rain from tbe register, 

 published by E. C. Giddy, Esq. of Penzance, in this Journal. 



