THE INNER PLANETS. 87 



Flammarion (born 1842), and others, under 

 less favourable climatic conditions, arrived at 

 a period of 24 hours. Aristarch Belopolsky 

 (born 1854), from spectroscopic observations at 

 Pulkowa, by means of Doppler's principle, found 

 a period of 12 hours. Lowell, by the same 

 principle, found, in 1901-03, a period of 225 

 days, in agreement with Schiaparelli's results. 

 This is the last word on the subject. Schia- 

 parelli's rotation period, confirmed by the theory 

 of tidal friction, is generally accepted. 



That Yenus has an atmosphere was one of 

 the conclusions reached by Schroter in 1792 ; 

 and in this at least he was correct, as the 

 atmosphere of Yenus, illuminated by the solar 

 rays, has been seen extending round the entire 

 disc of the planet. Spectroscopic observations 

 by Tacchini, Ricco, and Young, during the 

 transits of 1874 and 1882, indicated the exist- 

 ence of water-vapour in the planet's atmosphere. 

 Yery little has been discovered regarding the 

 " geography" of Venus. White patches at the 

 supposed "poles" of the planet were observed 

 in 1813 by Franz von Gruithuisen, and in 1878 

 by the French astronomer Trouvelot (1827-1895). 

 The secondary light of Venus, similar to the 

 " old Moon in the new Moon's arms," was 

 repeatedly observed since the time of Schroter 



