INEQUALITY IN RAINFALL. 163 



ence of a rainfall-inequality depending upon the state of 

 the sun. Dr. Meldrum began by pointing out that in a 

 good many places there is a greater rainfall during years 

 of maximum than during years of minimum sun-spots, 

 and that this phenomenon repeats itself from one solar 

 cycle to another. Again^ Governor Rawson has pointed 

 out the existence of certain localities where the rainfall- 

 inequality appears to be o£ a precisely opposite character, 

 while Dr. Hunter has showed the practical importance of 

 the investigation with reference to certain tropical stations. 

 The subject has likewise been discussed by Smyth^ Stone, 

 and others. 



r 5. The question has arisen whether it might be possible 

 to throw any light on this problem by the method of 

 detecting unknown inequalities, proposed by Mr. Dodgson 

 and myself (see ' Proceedings ' of the Eoyal Society, 

 May 29, 1879). The essence of this method consists in a 

 way by which we may numerically estimate the indica- 



. tions of an inequality. Let us suppose for instance that, 

 in ignorance of the diurnal range of temperature, we try 

 to find whether there be a temperature-inequality of 24 

 hours or whether there be not rather one of 26 hours. We 

 should begin by taking a large number of hourly readings 

 of temperature; and we should group these into two series, 

 the one containing 24 numbers in each horizontal row, 

 and the other 26. We should thus have 24 vertical 

 columns from the one series and 26 from the other; and 

 we should take the mean of each vertical column of each 

 series as well as the mean of the whole. 



Now it would speedily be found that an inequality was 

 indicated by the 24-hourly series and none by that of 26 

 hours. For in the first series the mean of the vertical 

 column representing observations at 5 a.m. would be 

 greatly less than the mean of the whole, while the mean 



m2 



