Mr. J. A. Broun on the Sun-spot Period and the Rainfall. 477 



difference of about 2 inches of rain may be expected betwixt 

 years of greatest and least spot-area. 



This result is derived from observations at ten stations, dis- 

 tributed over a very small patch of the earth's surface ; and it is 

 evident that for any serious investigation a much larger series of 

 observations representing the rainfall over a great extent of country 

 would be essential. 



I now examined observations made at different stations in 

 India ; but this examination showed the extreme difficulty of 

 obtaining a satisfactory result, either way, from a few stations in 

 that country, when, in certain years, the accidental excess of 

 rainfall at some of the stations may be 40 inches, even though 

 deficiencies at some stations may diminish the amount of the 

 error. 



Prom my own experience of rainfall on the Indian ghats, I 

 should doubt that a mountain-station, such as Mussoorie, is well 

 fitted to be employed in this discussion. If a single station could 

 be taken to represent any tract of country, it ought to be one least 

 liable to local causes of variation. Among the mountains a slight 

 change in the average direction of the wind will cause great 

 differences in the rainfall at stations but little distant from each 

 other, and to eliminate accidental variations of 40 or 80 inches 

 would require observations during a very long series of years. 



The following Table will, however, show the quantities which 

 may have to be dealt with at an Indian hill-station f : — 



Values of AR for Mahabuleshwar, 4500 feet above the sea, 

 with the corresponding values of AA. 



Year. 



AA. 



AE. 



Year. 



AA. 



AE. 



1832. 



-359 



in. 

 -26-1 



1843. 



-540 



in. 



+32.7* 



1833. 



-558 



-49-3 



1844. 



-465 



+ 9.3* 



1834. 



-506 



+ 44-3* 



1845. 



-232 



- 3-1 



1835. 



+ 171 



-26-3* 



1846. 



- 5 



+ 35-3* 



1836. 



+ 746 



- 9-4* 



1847. 



+ 469 



-34-2* 



1837. 



+ 556 



+ 14-8 



1848. 



+ 395 



- 8-0* 



1838. 



+ 293 



-72-8* 



1849. 



+203 



+ 85-4 



1839. 



+ 164 



-19-8* 









1840. 



- 46 



+ 31-4* 









1841. 



-306 



+ 28-0* 









1842. 



-429 



+ 51-9* 









From this Tabje-we derive the equation] 



AE=-0-02in. AA, 



or that 26 inches more rain falls for the year of least than for 



• ' f For the rainfall at Mahabuleshwar, see Colonel Sykes's paper on Indian 

 observations, Phil. Trans. 1850, p. 367. The mean fall is 253'0 inches. 

 * Indicates opposite signs of AA and AE. 



