THE SUN AND SUNSPOTS, 1820-1920 1 



By E. Wai/teb Maunder 



[With 7 plates] 



The Royal Astronomical Society was founded in 1820. At that 

 date it was known that there was a sun, that sometimes there were 

 spots upon its surface, and that the sun rotated on its axis. Prac- 

 tically that was all. 



In 1826, the systematic study of the sun's surface was commenced 

 by Schwabe, and it has been continued up to the present time. 

 Schwabe presented his drawings to the Royal Astronomical Society ; 

 and as it also possesses those of some of his predecessors in the same 

 field, this society now holds records of one kind or another showing 

 the changes that have taken place upon the solar surface from the 

 year 1820, and so continuously to the present date. 



The question before us this evening is : What views do we now hold 

 of the constitution of the sun and the relationships of its spots, and 

 upon what facts do we base them ? 



A quarter of an hour is a short time in which to review the scien- 

 tific evolution of a century, even when the inquiry is restricted to a 

 single department of astronomy, so confined that it deals only with 

 sunspots as drawn at the telescope, or impressed upon the photo- 

 graph plate. 



My first illustration (fig. 1) deals with the annual percentages of 

 spotless days, 1826-1923, and is an extension of that appearing in the 

 Monthly Notices, 74, Plate 4, between pages 114 and 115. It is based 

 upon Schwabe's persistent daily count of sunspots. In itself, his 

 work was very simple and straightforward, but it was carried on 

 systematically and with the utmost patience. These qualities made 

 it great and epoch making, and they were acknowledged by the 

 award to him, in 1857, of the gold medal of this society. 



The diagram is deduced, partly from the observations of Schwabe ; 

 partly from those of R. Wolf; and from 1885 to the present time 

 from the Greenwich Photoheliographic Results. It exhibits for each 



1 An address given on the evening of Monday, May 29, 1922, at the conversazione held 

 in connection with the centenary of the Royal Astronomical Society. Reprinted by per-, 

 mission from Monthly Notices of the Royal Astronomical Society, Vol. LXXXII, No. 9. 

 With additions. 



159 



