THE RAINFALL OF CORNWALL. 295 



40 feet above sea level.^'*' No guage seems from that time to 

 have been at work until 1835, but in th; ^ year the record for 

 Kimberley Place, Falmouth commences ; in 1837 and 1838 the St- 

 Breock and Eoyal Institution returns begin, and in 1840 the Hel- 

 ston Guage was established ; these two last being the largest 

 continuous records in the county, the former extending over 36 

 years and the latter over 33. After 1840 Observers gradually in- 

 creased, until now they number more than 40, whilst numerous 

 registers have been kept for short periods although now discon- 

 tinued. 



It is, however, essential that to obtain trustworthy results a 

 register of the rainfall should have been kept for a sufficient 

 length of time, that is for a period of about 20 years, but the 

 number of guages which have been at work for that length of 

 time bears only a small proportion to the number from which I 

 have collected returns. I have, therefore, in deducing the mean 

 Annual Rainfall, taken the observations of this Institution as a 

 standard ; calculated the proportion with the average rainfall of 

 the years during which each guage was at work bears to the 

 Mean Annual Rainfall of the 36 years of the standard, and 

 reduced the various returns accordingly ; thus obtaining a much 

 nearer approximation to the Rainfall at Stations at which obser- 

 vations have only been taken for a very short time, which 

 otherwise would be practically useless in determining the average 

 fall of rain in the districts in which they are situated. 



Table No. 1. gives the details of the Monthly and Annual 

 Falls of Rain for the last 36 years at the Royal Institution of 

 Cornwall, and the diagram. Fig. 1 shows an analysis of the 

 yearly falls for the same period. 



The Mean Annual fall for 36 years is 42-07 Ins., whilst the 

 maximum and minimum falls are 60" 12 and 29 "43 Ins., occurring 

 respectively in the years 1841 and 1870. The variations in 

 different years are clearly shown in the diagram ; and in the 

 Table No. 2. the fluctuations at Truro and Greenwich (which I 

 have added for comparison) are expressed in percentages of the 

 Mean Annual Rainfall. 



** Beardmore's Manual of Hydrology, p 298. 



