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Mr. Henwood on Periodical Variations 



deavour, as briefly as I can, to supply other matter, which I 

 was prevented from giving in that paper, by circumstances 

 not under my own control. The observations to which I now 

 venture to solicit your attention, extend through seven years ; 

 from IS'iS to 1829 both inclusive. The first inquiry seems to 

 be, " For the same mine the depth being constant, what is the 

 variation in the quantity of water delivered, for corresponding 

 months of various years ?" The examples I select, are the 

 United Mines, situated in slate, depth from which the water is 

 drawn 98 fathoms; Dolcoath, of which the surface is slate, 

 and the bottom granite, water drawn from 222 fathoms deep ; 

 and Huel Damsel, situated in granite, depth 202 fathoms. 

 For further details of the depth, and mode of estimating the 

 water, I refer to my former paper*. The following Table I. 

 represents the mean of the average monthly quantities of water 

 pumped out of these mines, in cubic feet, and the monthly 

 averages of rain in inches for the same periods. 



Table I. 



Taking the foregoing means respectively as standards of com- 

 parison, we shall see how the monthly averages in the follow- 

 ing Table II. vary therefrom. 



* Phil. Mag. and Annals, N.S. vol. ix. p. 171. 



