472 



On the Sun-spot Period and the Rainfall. [June 18, 



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. 



From my own experience of rainfall on the Indian ghats, I should 

 doubt that a mountain-station, such as Mussoorie, is w r ell fitted to be 

 employed in this discussion. If a single station could be taken to repre- 

 sent 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 direc- 

 tion 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 AB, for Mahabuleshwar, 4500 feet above the sea, with the 

 corresponding values of AA. 



Prom this Table we derive the equation 



AB=-0-02in. AA, 



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

 greatest spot-area. The examination of many series of observations has 

 shown how difficult it will be to arrive at a conclusion for a quantity so 

 small as 2 inches of rain. 



It is evident that a larger tract of country than Great Britain should 

 be chosen, and the approximate rainfall be deduced from the greatest 



f For the rainfall at Mababuleshwar, see Colonel Sykes's paper on Indian observa- 

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

 Indicates opposite signs of AA and AE. 



