MR. J. HEAP ON THE RAIN-FALL AT OLDHAM. 



339 



assuming the height of the gauge to be 1 1 feet above the 

 ground^ it would give 39*752 inches for the mean rain-fall 

 at Oldham for 27 years. Although Oldham is fully 200 feet 

 higher than Bolton, the rain-fall at Oldham is greatly below 

 that at Bolton : for example, the rain-fall at these two sta- 

 tions in i860, 1 86 1, and 1862 was as follows : — 





i860. 



1861. 



1862. 



Oldham 



inches. 

 44-023 

 57-660 



inches. 



33*084 

 44-910 



inches. 

 41-238 

 53'43o 



Bolton 



Difference 



13-637 



11-826 



12-192 



or a mean difference of 12*551 inches. The data at Bolton 

 are from Mr. H. H. Watson^s returns, 290 feet above the 

 sea, and 3f feet above the ground. No doubt the greater 

 fall at Bolton is owing to the vicinity of high lands, in- 

 cluding the large mass of Kivington Pike. Part of these 

 differences is caused by the gauge at Oldham being placed 

 7 1 feet above that at Bolton, referred to the surface of the 

 earth as datum. The values for the mean rain-fall at Old- 

 ham for 27 years, given in Vol. Ill of the Proceedings of 

 our Society, page 112, are too small, owing to the great 

 height the gauge was placed above the ground during the 

 first seventeen years. Mr. Heap informs me that, from 

 the beginning of the present year, his gauge has been lowered 

 to 4 feet above the ground. 



The Tables appended to this paper are, ist, monthly fall 

 for 27 years at Oldham ; 2nd, comparative annual falls at 

 Oldham and Manchester ; 3rd, mean monthly rain-fall at 

 Oldham during each period that the same gauge and system 

 of measurement was adopted. 



z 2 



