THE SUN, 59 



Observatory from 1858 to 1888, when he was 

 appointed director of the Observatory at Upsala. 

 In that year he commenced a study of the solar 

 rotation, measuring it by means of Doppler's 

 principle. He confirmed the telescopic work 

 of Carrington and Sporer on the equatorial 

 acceleration, and measured the displacement up 

 to within fifteen degrees of the poles. He 

 brought out the surprising fact that the rota- 

 tion period of the Sun is there protracted to 

 38^ days. These remarkable researches were 

 published in 1891. 



In 1873 the Astronomer -Royal of England 

 commenced at Greenwich Observatory to photo- 

 graph the Sun daily. This work has been 

 carried on there by Edward Walter Maunder 

 (born 1851), and Greenwich Observatory pos- 

 sesses a photographic record of sun-spots. At 

 the Meudon Astrophysical Observatory, near 

 Paris, Janssen has, since 1876, secured photo- 

 graphs of the solar surface, which were com- 

 prised in a great atlas, published by him in 

 January 1904. These photographs have re- 

 vealed a remarkable phenomenon the " reseau 

 photospherique," the distribution over the solar 

 surface of blurred patches of light, which 

 Janssen considers are inherent in the Sun. 

 The Greenwich records of sun - spots and of 



