ON THE RAINFALL IN THE BRITISH ISLES. 



173 



■wards the collection of old observations. It is a most desirable object, and 

 without it our other work will not be complete ; but our Secretary has not 

 time for it, and we have not funds to provide a regular copyist. 



In our last Report^ we gave an analysis of the results of the experimental 

 gauges employed at Calne to determine the relative indications of gauges of 

 various sizes. 



We now give a similar discussion of the series erected to test the influence 

 of elevation above the ground on the amount collected. It had long been known 

 that gauges on buUdinr/s collected considerably less than those on the ground, 

 this branch of the inquiry having many years ago been examined with great 

 care by Prof. Phillips. As his experiments and results are printed in the 

 3rd, 4th, and 5th Reports of this Association, it is unnecessary here to give 

 more than a brief resume of the whole. Prof. Phillips had three similar 

 gauges, one placed in the gardens of the York Museum, one on its roof, and 

 one on a pole 9 feet above the battlements of the great tower of York 

 Minster. The heights of these gauges, the total amounts collected, and their 

 ratios are given in the following Table : — 



Heiglit 



Above ground 



„ bigb water 



Total of 12 montlis, 1832-33 



1833-34 



1834-35 



„ for 3 years 



1832-33 



"833-34 



1834-35 



3 years 



Ground. 



ft. in. 



o 2 

 29 o 



Museum. 



ft. in. 

 43 8 



72 8 



Minster. 



ft. 



212 



241 



m. 

 10 

 10 



Amount of 



Ratio. 



m. 



2379 



25-71 



1 5 94 



65-44 



1 00-0 

 loo-o 

 loo-o 

 loo-o 



in. 



20-18 



19-85 



12-14 



52-17 



853 



77-2 

 76-1 

 797 



m. 



15-72 



14-96 



8-29 



38-97 



66-1 

 58-2 

 52-0 

 59-6 



Wc need hardly remark that, owing to the labour of ascending to the 

 top of the Minster, the observations were not taken daily, but about once a 

 month. The result of a series of calculations was to indicate that the nor- 

 mal rate of decrease was not very far from 3 \/ h, but that both the actual 

 amount and the ratios were dependent on temperature. 



The Calne experiments, of which we are now going to give a brief account, 

 differed from those of Prof. Phillips, both in their object and their details. 

 At York the object seems to have been to determine the causes of the dif- 

 ferent amounts collected ; at Calne it has been to ascertain the precise dif- 

 ferences, and the possibility, or otherwise, of deducing corrections whereby 

 observations made at various small heights above the ground may be reduced 

 to one common standard. Hence the gauges were mounted on posts, not on 

 roofs ; the greatest height was 20 feet instead of 210 feet, and the readings 

 were taken daily instead of monthlj^. It may be expedient, before proceed- 

 ing further, to illustrate by an example the necessity for this correction — 

 (1) on account of its extent, (2) on -account of the very various heights at 

 which gauges are placed. Taking haphazard a single page of British Hain- 

 fall, which contains returns from 44 stations, we find just 22 different 

 heights, viz. : — 



