THE INNER PLANETS. 81 



transit over the Sun's disc. Le Verrier, certain 

 that this was the missing planet, named it 

 "Vulcan," and calculated its orbit, assigning it 

 a revolution period of twenty days. But it was 

 never seen again. Transits of "Vulcan" were 

 fixed for 1877 and 1882, but nothing was seen 

 on these dates. During the total eclipse of 

 July 29, 1878, two observers James Watson 

 (1838-1880), the well-known astronomer, and 

 Lewis Swift (born 1820) believed themselves 

 to have discovered two separate planets, and 

 ultimately claimed two planets each, which were 

 never heard of again. During the total eclipse 

 of 18 83 an active watch for " suspicious objects " 

 was kept, but with no result. At the eclipses 

 of 1900 and 1901 respectively, photographs were 

 exposed by the American astronomers, W. H. 

 Pickering and Charles Dillon Perrine (born 

 1867), but on none of these plates could any 

 trace of "Vulcan" be found. At the total 

 eclipse of August 30, 1905, plates were again 

 exposed, but no announcement has been made 

 of an intra-Mercurial planet ; and the prevalent 

 opinion among astronomers is that no planet 

 comparable with Mercury in size exists between 

 that planet and the Sun. 



The study of the physical appearance of 

 Mercury was inaugurated by Schroter, who in 



F 



