210 A CENTURY'S PROGRESS IN ASTRONOMY. 



amateur astronomer, who secured admirable 

 representations of clusters and nebulae. He 

 published, in 1893 and 1900, two volumes of 

 collected photographs of clusters and nebulae. 

 This monumental work was thus referred to by 

 Dr William James Lockyer : " Dr Roberts has 

 not only nobly enriched astronomical science, 

 but has raised a monument to himself which 

 will last as long as astronomy has any interest 

 for mankind." 



Perhaps the most remarkable revelation made 

 by photography in this branch of research has 

 been the discovery of the nebulae in the 

 Pleiades. In 1859 Tempel observed at Flor- 

 ence an elliptical nebula south of the star 

 Merope. On November 16, 1885, the brothers 

 Henry obtained at Paris a photograph of the 

 Pleiades, revealing the existence of a small 

 spiral nebula. This was confirmed by visual 

 observations, and particularly by the photo- 

 graphs of Roberts, which also showed the entire 

 cluster to be nebulous, and that " the nebulosity 

 extends in streamers and fleecy masses, till it 

 seems almost to fill the spaces between the stars, 

 and to extend far beyond them." In 1888 a 

 further advance was made by the brothers 

 Henry, who found seven stars to be strung on 

 a nebulous streak. 



