THE MEASUREMENT OF KAIN. 11 



The following observations upon the fall of rain and the 

 quantity of water flowing off the ground, are from measure- 

 ments taken in the course of the enquiries made during 

 the last few years, with reference to the supply of Man- 

 observations conducted by him. It contains the following judicious and 

 important remarks in reference to the points just alluded to : — 



" In the last Report I observed, ' it would be premature, from the scanty 

 data before me, to draw any conclusion as to the gradation in the quantity 

 of rain at the great elevations al)ove the sea. But it seems probable that, 

 in mountainous districts, the amount of rain increases from the valley 

 upwards, to an altitude of about 2000 feet, where it reaches a maximum ; 

 and that above this elevation the quantity rapidly decreases.' 



" The Table for 1846, exhibited the rain fall of the siunmer months 

 only, but the additional returns of 1847, obtained in every variety of 

 season, confirm the above deductions in every essential particular ; so that 

 we may fairly assume the combined results to be indicative of a physical law, 

 so far, at least, as relates to the particidar locality in question. Thus in 

 twenty-one months, 



The Valley 160 feet above sea, has received 170"65 inches. 



„ Stye-Head 1290 „ „ 186-74 



„ SeatoUar 1334 „ „ *180'28 



„ SparkUngTaru 1900 „ „ 20791 



„ Great Gabel... 292.'> „ „ 136-98 



„ Sea Fell 3166 „ „ 12815 



" An apparent exception to this law occurs at the gauge stationed at 

 Burnt Rigg, about midway between the top of Stye-Head and the vale of 

 Wast dale, and which in 1847 has received about one- eighth, or twelve 

 and three quarters per cent., less rain than the valley. 



" This is the only one of the gauges situated on the slope of a mountain ; 

 it is on the windward side, and I imagine that in such a position, eddies or 

 counter-currents are produced in windy weather which cause a less quantity 

 of water to be deposited in the instrument than is due to the elevation. 

 We know that all sloping roofs, from the same cause, materially diminish 

 the receipts of rain gauges. 



" It will be observed that the amount of water received by the Seatollar 

 gauge, is invariably less than the deposit in the adjacent vale of Sea- 

 thwaite, and the deficiency is pretty equable in every month of the year. 

 •' I am -unable to give any satisfactory reason for this anomaly, or to 



* The height of Seatollar common has not been accurately asoertained. 



