NOTICES AND ABSTRACTS 



OF 



MISCELLANEOUS COMMUNICATIONS TO THE SECTIONS. 



MATHEMATICS AND PHYSICS. 



Address hy Professor Balfour Stewart, M.A., LL.D., F.E.S., President of 



the Section. 



Since the last meeting of the British Association science has had to mourn the 

 loss of one of its pioneers in the deatli of the veteran astronomer Schwahe, of 

 Dessau, at a good old age, not before he had faithfully and honourably finished his 

 work. In truth this work was of such a nature that the worker could not be ex- 

 pected long to survive its completion. 



It is now nearly fifty years since he first began to produce daily sketches of the 

 spots that appeared upon the sun's surface. Every day on which the sun was 

 visible (and such days are more frequent in Germany than in this country), with 

 hardly any intermisssion for forty years, this laborious and venerable observer made 

 his sketch of the solar disk. At length this unexampled perseverance met with its 

 reward in the discovery of the periodicity of sun-spots, a phenomenon which very 

 speedily attracted the attention of the scientific world. 



It is not easy to overrate the importance of the step gained when a periodicity 

 was found to rule these solar outbreaks. 



A priori, we should not have expected such a phenomenon. 



If the old asti-onomers were perplexed by the discovery of sun-spots, their 

 successors must have been equally perplexed when they ascertained their periodicity. 



For while all are ready to acknowledge periodicity as one of the natural con- 

 ditions of teiTestrial phenomena, yet every one is inclined to ask what there can be 

 to cause it in the behaviour of the sun himself. 



Manifestly it can only have two possible causes. It must either be the out- 

 come of some strangely hidden periodical cause residing in the sun himself, or 

 must be produced by external bodies, such as planets, acting somehow in their 

 varied positions on the atmosphere of the sun. 



But whether the cause be an internal or external one, in either case we are 

 completely ignorant of its nature. 



We can easily enough imagine a cause operating from the sun himself and his 

 relations with a surrounding medium to produce great disturbances on his surface, 

 but we cannot easily imagine why disturbances so caused should have a periodicity. 

 On the other hand we can easily enough attach periodicitj^ to any effect caused by 

 the planets, but we cannot well see why bodies comparatively so insignificant should 

 contribute to such very violent outbreaks as we now know sun-spots to be. 



If we look within we are at a loss to account for the periodicity of solar dis- 

 turbances, and if wo look without we are equally at a loss to account for their 

 magnitude. 



1875. 1 



