ASTRO-PHYSICS 291 



milky way, we are looking towards the rim of 

 the lens, and therefore, owing to the greater 

 depth, see more stars. 



The appearance of temporary stars is a 

 phenomenon which has been observed repeatedly 

 in historical times. Hipparchus, Tycho Brahe, 

 and Kepler, for instance, have recorded such 

 manifestations. But the first case critically 

 examined by modern photographic methods was 

 that of Nova Aurigae, a star discovered in 

 February 1892, the origin and growth of which 

 were traced by subsequent examinations of 

 photographs taken in the previous December and 

 January, and preserved as part of the systematic 

 photographic log-book of the heavens now kept 

 by astronomers. For three months the star's 

 brightness lasted and then rapidly it decreased, 

 till at the end of April the Nova was barely 

 visible in the great refracting telescope of the 

 Lick Observatory. Soon afterwards, however, 

 a faint nebula appeared in its place, with a quite 

 different kind of spectrum. 



More completely studied were the striking 

 phenomena of the second Nova Persei, first 

 sighted at Edinburgh in February 1901. Its 

 rise and decline were followed in many places, 

 particularly by Father Sidgreaves at Stony- 

 hurst, and by Professor Campbell at the Lick 

 Observatory. It attained its maximum bright- 

 ness about a day and a half after its detection, 

 and then grew fainter in a fluctuating manner for 

 about ten days. Finally, a nebula was seen to 

 develop, which increased in visible dimensions 

 at a prodigious rate — so fast, indeed, that the 



