2 REPORT 1875. 



But since tliat witMn the sun is hidden from our view, it cannot surely be con- 

 sidered blameworthy if astronomers have directed their attention to that without, 

 and have endeavoured to connect the behaviour of sun-spots with the positions of 

 the various planets. 



Stimulated, no doubt, by the success which had attended the laboui-s of Schwabe, 

 an English astronomer was the next to enter the Held of solar research. 



The aim of Mr. Carrington was, however, rather to obtain very accurate record.s 

 of the positions, the sizes, and the shapes of the various sun-spots, than to make a 

 very extensive and long-continued series of observations. He was aware that a 

 series at once very accurate and very extended is beyond the power of a private 

 individual, and can only bo undertaken by an established institution. Nevertheless 

 each sun-spot that made its appearance during the seven years extending from the 

 beginning of 1854 to the end of 1860 was sketched by Mr. Carrington witli the 

 greatest possible accuracy, and had also its heliographic positions — that is to .say, 

 its solar latitude and longitude — accurately determined. 



One of the most prominent results of Mr. Carrington's labours was the discovery 

 of the fiict that sun-spots appear to have a proper motion of their own, those 

 nearer the solar equator moving faster than those more remote. Another was the 

 discovery of changes apparently periodical atfectiug the disposition of spots in 

 solar latitude. It was already known that sun-spots confined themselves to the 

 sun's equatorial regions ; but Mr. Carrington showed that the region affected was 

 liable to periodical elongations and contractions, although his observations were not 

 sufficiently extended to determine tlie exact length of this period. 



Before Mr. Carrington had completed his seven years' labours, celestial photo- 

 gi-aphy had been introduced by Mr. Warren Ue La Rue. Commencing with his 

 private observatory, he next persuaded the Kew Committee of the British Associa- 

 tion to allow the systematic photography of the sun to be carried on at their 

 observatory under his superintendeuce, and in the year 1862 the lirst of a ten j'ears' 

 series of solar photographs was begun. 



Before this date, however, Mr. De La Rua had ascertained, by means of his 

 photoheliograph, on the occasion of the total eclipse of LS60, that tlie red promi- 

 nences surrouuding the eclipsed sun belong, without doubt, to our luminary himself. 



Tlie Kew observations are not yet finally reduced, but already several importaut 

 conclusions have been obtained from them by Mr. Do La Rue and the other Kew 

 observers. In the first place the Kew photographs confirm the theory of Wilson 

 that sun-spots are phenomena the dark portions of which exist at a level consider- 

 ably beneath the general sm'face of the sun— in other words, they are hollows or 

 pits, tlie interior of which is of course tilled up with the solar atmosphere. The 

 Kew observers were likewise led to associate the low temperature of the bottom of 

 sun-spots with the downward carriage of colder matter from the atmosjihere of the 

 sun, while the upward rush of heated matter was supposed to account for the 

 faculse or bright patches which almost invariably accompauj' spots. In the next 

 place, the Kew observers, making use not only of the Kew series but of those of 

 ydiwabe and Carrington, which were generously placed at their disposal, have dis- 

 covered traces of the influence of the nearer planets upon the beliaviour of sun- 

 spots. This influence appears to be of such a natiu-e tliat spots attain their maxi- 

 mum size when carried by rotation into positions as far as possible remote from 

 the intiueuciug planet — that is'to say, into positions where the bodj^ of the sun is 

 between them and the planet. There is also evidence of an excess of solar action 

 when two influential planets come near together. But although considerable light 

 has thus been thrown on the periodicity of sim-spots, it ought to be borne in mind 

 that the cause of the remarkable period of eleven years and a quarter, originally 

 discovered by Schwabe, has not yet been properly explained. The Kew observers 

 have likewise discovered traces of a peculiar oscillation of spots between the two 

 hemispheres of the sun ; and finally their researches will place at the command of 

 the observers the data for ascertaining whether centres of greater and lesser solar 

 activity are connected with certain heliocentric positions. 



While the sun's surface was thusljeing examined both telescopically and plioto- 

 graphically, the spectroscope came to be emploj-ed as an instrument of reseai'ch. It 

 had already been sm-mised by Professor Stokes that the vapom of sodium at a 



