88 A CENTURY'S PROGRESS IN ASTRONOMY. 



by Vogel, Lohse, Zenger, and others. Vogel 

 attributed it to twilight, and Lamp, a German 

 observer, to electrical processes analogous to our 

 aurorse. In 1887 a Belgian astronomer, Paul 

 Stroobant, submitted to a searching examination 

 all the supposed observations of a satellite of 

 Venus, and was enabled to explain nearly all 

 the supposed satellites as small stars which 

 happened to lie near the planet's path in the 

 sky at the time of observation. 



The study of our own planet can hardly be 

 said to belong to the realm of astronomy. 

 Nevertheless, it is through astronomical observa- 

 tion that the motion of the North Pole has been 

 discovered. For many years it has been a 

 problem whether there is a variation of latitude 

 resulting from the motion of the pole. Euler 

 had declared, from theoretical investigation, that, 

 were there such a motion, the period must be 

 10 months. The question was revived in 1885 

 by the observations of Seth Carlo Chandler 

 (born 1846) at Cambridge, Mass., with his 

 newly -invented instrument, the " almucantar," 

 which indicated an appreciable variation of 

 latitude. This was confirmed by Friedrich 

 Kiistner (born 1856), now director of the 

 Observatory at Bonn. The idea now occurred 

 to Chandler to search through the older records 



