706 THE UNIVERSE. 



ready to take a note of them. " Be ready to write," he 

 would say ; " the nebulae are coming." 



The Clouds of Magellan, those luminous patches which 

 cover so large a space in the southern region, and look like 

 rags torn from the Milky Way, present a complex composi- 

 tion, being analogous to a certain extent with the nebulae. 

 Sir John Herschel says they are formed of isolated stars, of 

 swarms of stars, and, lastly, of nebulae, more compact than 

 those which we find near the Virgin and in the Tresses of 

 Berenice. 



The first mariners who ventured into the southern seas 

 were also struck by certain phenomena of a totally opposite 

 character ; these were black patches irregularly outlined on 

 the vault of the heavens, to which, in their imaginative lan- 

 guage, they gave the name of coal-sacks. According to as- 

 tronomers, these patches, the most celebrated of which are 

 near the Southern Cross, are due to the sky being at these 

 parts to a great extent without stars. They seem to be 

 really holes, according to the expression of Humboldt, by 

 means of which our vision pierces into the remotest spaces 

 of the universe. 



