ON THE LONG-PERIOD INEQUALITY IN RAINFALL. 161 



XVIII. On the Long-period Inequality in Rainfall. By 

 Balfour Stewart, LL.D., F.R.S., Professor of Na- 

 tural Philosophy at the Owens College, Manchester. 



Read February 24th, 1880. 



1 . If it be true that there is a variation in the power of 

 the sun depending on the state of his surface, this varia- 

 tion might naturally be expected to make itself apparent 

 through a corresponding change in the rainfall of the 

 earth ; so that when the sun is most powerful there ought 

 to be the greatest rainfall. 4 



2. While the connexion indicated above is that which 

 most readily occurs to the mind, yet the difficulty of 

 ascertaining the facts of the case in a manner bearing the 

 smallest approach to completeness is so great as to be at 

 present insuperable. 



There is first of all an intense reference to locality in 

 rainfall, so that the rainfall at one place may differ greatly 

 from that at another place in its near neighbourhood. 

 Again, there are probably, in addition to possible secular 

 inequalities, very great oscillations in the yearly rainfall at 

 any one place, or accidental variations, as we may term 

 them in our ignorance of their cause. 



Thirdly, it is in comparatively few places, and those 

 places chosen without the smallest reference to this par- 

 ticular problem, that we have any thing like a trustworthy 

 account of the rainfall throughout a considerable number 

 of years. 



ser. III. vol. Vll. M 



