1 70 Mr. Hen wood's Facts bearing on the Theory of theFormation 

 Describe from s as pole the circle / o , then is o m the third cor- 



rection. Draw at m a tangent and make T I = tang D, then is 



sin T = sin / m . cotang D. 



but mo. sin 1" = tang D (1 cos T) = tang D . 2 sin 2 T 

 4 tang D 4 sin 2 | T = | tang D (2 sin J T) 2 = tang D sin 2 T 



= i tang D cotang 2 D sin 2 Im = sm * L l ~ s 1 . 



2 tang D 



Hamburgh, Jan. 16, 1831. C. RuMKER. 



XXXI. Facts bearing on the Theory of the Formation of 

 Springs, and their Intensity at various Periods of the Year. 

 By W. J. HENWOOD. 



r |^HAT those springs which exist during the winter and dis- 



-* appear as summer approaches, owe their origin to rain, 



has not I believe been disputed. But whether we may ascribe 



to the same cause those on which changes of the seasons ap- 



?ear to exert but little influence, has been frequently discussed, 

 n the mining districts of Cornwall, registers of the perform- 

 ance of the steam-engines employed for pumping water, is 

 periodically published by Messrs. John and Thomas Lean, of 

 Camborne. These documents supply information from which 

 it is not difficult to calculate the quantity of water drawn by 

 each engine in a' month, and consequently the intensity of 

 springs at the spot. The particulars contained in the follow- 

 ing columns are of some consequence in this investigation. 



In some of the extensive mines several steam-engines are 

 required ; and as they are usually erected at a considerable di- 

 stance from one another, each drains the whole of a certain 

 district. Hence I think we may safely assume the water drawn 

 by one engine as representing the intensity of the springs 

 at that spot. The numbers in Table I. denote cubic feet of 

 water drawn by one engine; in Table II. the averages of the 

 respective mines are for one engine on each ; but in Table III. 

 the numbers are intended for cubic feet of water drawn by all 

 the engines on each of the respective mines. 



Mine 



