334 MR. G. V. VERNON ON THE NUMBER OF DAYS 



be found that, when rightly considered in relation to dis- 

 turbing causes, even these will tend indirectly to confirm 

 the method of grouping the data of tidal hours in relation 

 to land- areas as causal centres. 



XXV. — On the Number of Days on which Rain falls 

 annually at London, from observations made during the 

 fifty-six years, 1807 ^^ 1862. By G. V. Vernon, Esq., 

 F.R.A.S., M.B.M.S. 



Read before the Physical and Mathematical Section, April 30th, 1863. 



Being frequently asked by medical men and others on 

 what number of days rain usually falls during the year, I 

 have compiled the Table accompanying this paper. 



The observations made at Somerset House by the Royal 

 Society for the years 1797 to 1830 being in many months 

 not trustworthy (see Howard^s * Climate of London,' 2nd 

 edition, vol. i. p. 132), I have adopted Howard's values 

 for the years 1807 to 1831, given in his ^ Climate of Lon- 

 don,' vol. i. These observations, although not made ab- 

 solutely in London, may safely be used without any great 

 error being introduced. From 1832 to 1840 I have 

 adopted the values given for Somerset House, printed 

 in the '^Philosophical Transactions.' From 1841 to 1862 

 the values are those for Greenwich Observatory. Through- 

 out the entire period of 56 years, there is not a single 

 month in which no rain fell. 



The years in which rain fell upon the fewest days were 

 1832 and 1834, the numbers being 86 and 82 days respect- 

 ively; 1832 was the cholera year. Rain fell upon the 

 greatest number of days in 1848, the number being 223 

 days. The mean number of days upon which rain fell 



