148 A CENTURY'S PROGRESS IN ASTRONOMY. 



have been found in positions which clearly in- 

 dicate that they must have fallen from the sky. 

 Chemists have made analyses of the elements in 

 these remarkable bodies, and have found them 

 to contain iron, magnesium, silicon, oxygen, 

 nickel, cobalt, tin, copper, &c. The spectrum 

 of these aerolites, raised to incandescence, has 

 been studied by Vogel and by the Swedish 

 observer, Bernhard Hasselberg (born 1848), who 

 detected the presence of hydrocarbons, which are 

 also present in cometary spectra. 



When the existence of aerolites as celestial 

 bodies was first recognised, Laplace suggested 

 that they had been ejected from volcanoes on 

 the Moon. This theory, although supported 

 by Olbers and other astronomers, was soon 

 rejected. Next, it was suggested that they 

 were ejected from the Sun, and Proctor believed 

 them to come from the giant planets. A very 

 detailed discussion of the subject is to be found 

 in Ball's ' Story of the Heavens' (1886), in which 

 he expresses views in harmony with those of 

 the Austrian physicist Tschermak. Ball demon- 

 strated that the meteors which fall to the Earth 

 cannot have come from any other planet, nor 

 from the Sun. Accordingly, he concluded that 

 they were originally ejected by the volcanoes 

 of the Earth many ages ago, when they were 



