1880.] 



Inquiry into the Periodicity of Rainfall. 



78 



eleven, or twelve years, this method of treatment shows it to be com- 

 pletely masked (in a long series of observation) by other variations. 



The discrepancies exhibited in the first tables obtained made it very 

 desirable to extend the field of inquiry, by including as many obser- 

 vations in the discussion as possible ; but having fixed upon the 

 arbitrary limit of fifty years as the least number of years of observa- 

 tions suitable for dealing with after my method, the materials for 

 doing so were not very abundant. Eventually I was able to collect 

 the following ten series : — 



Station. 



Periods. 



No. of 

 years. 



Authority. 



Paris 



Padua 



England (Sy 

 mons' table) . 



Milan 



London 



Madras 



Philadelphia . 

 Edinburgh . . . 



New Bedford . 

 Pvome 



1689—96, 1699—1754, 

 1773—97, 1804—75 



1725 to 1878 



1726 to 1865 



1764 to 1878 



1813 to 1878 



1813 to 1877 



1810 to 1867 



1822 to 1878 



1814 to 1867 



1825 to 1878 



161 

 154 



140 

 115 

 66 

 65 



58 

 57 



54 

 54 



Annuaire de l'obserratoire 



cle Montsouris, 1879 

 MSS. from P. Denza 



j B. A. Eeport, 1866 

 MSS. from P. Denza 

 Dines and Symons 

 " Nature," vol. sviii, p. 

 565 



Smithsonian Tables, p. 97 

 " Nature," vol. xyiii, p. 

 97 



Smithsonian Tables, p. 90 

 MSS. from P. Denza 



To these I added an eleventh one, forming a series by combining 

 together the annual rainfall for 1822 to 1875 at Loudon, Paris, and 

 Edinburgh. This increased the total number of years of observations 

 used in the discussion to 978. 



The result of the extended investigation in no way affected the con- 

 clusion pointed out by the observations previously treated, viz., that 

 taking the series of annual totals directly as they stand, there is no 

 marked indication of the presence of a short cycle to be found. 

 There are a few exceptions, notably in the case of the nine-year period 

 for New Bedford, and Philadelphia, the eleven-year cycle for Madras, 

 and the ten-year cycle for London, Paris, and Edinburgh combined, 

 in all of which cases the coincidences but slightly preponderate over 

 the non-coincidences. 



Again on consideration of the differences in Tables I to IX, it will 

 be seen that for the same epoch the curves of variation differ widely 

 for localities comparatively close together. For example, taking the 

 eleven-year cycle for Padua and Milan, stations only about 130 miles 

 apart, both well situated for observing rain, and no mountain range 

 intervening, the variation curves are as follows : — 



