[ 474 ] 

 LV. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 326.] 



June 18, 1874. — Joseph Dalton Hooker, C.B., President, in the 



Chair. 



''pHE following communication was read : — 



, , " On the Sun-spot Period and the Eainfall." By J. A. Brouri, 



F.K.S. 



Having read with much interest Mr. Meldrum's communication 

 to the Royal Society on the apparent simultaneity of excess of 

 rainfall and sun-spot area*, I have waited some confirmation of 

 his conclusions from a more extensive induction. Mr. Hennes- 

 sey's "Note" in the Proceedings of the Society for April 1874 f 

 induces me to offer the following views and results to the Eoyal; 

 Society. 



It is well known that the amount of rainfall is a very variable 

 quantity in some countries and in certain positions, and that 

 when there is a year of drought in one part of the world, there is 

 frequently an excess of rain in another. Any investigation, then, 

 which should be occupied with the average fall of rain over the 

 earth's surface must be long and laborious, unless the variation 

 to be dealt with is large and marked compared with others which 

 must be considered purely accidental relatively to the sun's spots. 

 In proof of this I may cite the rainfall at Mussoorie given by Mr. 

 Hennessey i, where, as far as the sun-spot area is known, any 

 result favourable to the connexion of the two phenomena 

 depends wholly on the rainfall for 1861, which is upwards of 50 

 inches in excess of the mean. If this excess be not due to the 

 great spot-area, then a long series of years' observations might be 

 requisite to make the positive and negative errors destroy each 

 other. 



It has been with the intention of determining what may be the 

 effect of a given change of sun-spot area, within a limited district, 

 during a period favourable to the connexion of the two phe- 

 nomena, that the following discussions have been made. We can 

 then say approximately within what limits the excess and defi- 

 ciency of rainfall lie for the years of greatest and least spot-area, 

 what amount of observations may be required to destroy acci- 

 dental variations, and whether the result may encourage more 

 extensive research. 



Mr. Meldrum finds a mean difference of 8*5 inches of rain be- 

 tween the falls for the years of greatest and least spot-area § ; 

 but this result is derived to some extent from short series of obser- 

 vations made in different parts of the world, and gives no weight to 

 the rainfall in other years than those considered years of maximum 

 or minimum sun-spots. 



* Proceedings of the Royal Society, vol. xxi. p. 297. 



t Ibid. vol. xxii. p. 286. |J Ibid. vol. xxii. p. 287. § Ibid. vol. xxi. p. 305. 



