114 A CENTURY'S PROGRESS IN ASTRONOMY. 



resembling those of Jupiter were observed by 

 Young at Princeton in 1883. In the following 

 year Paul and Prosper Henry discerned at Paris 

 two grey parallel lines on the disc of the planet. 

 This was confirmed by the observations of Per- 

 rotin at Nice, which also indicated rotation in a 

 period of ten hours. In 1890 Perrotin again took 

 up the study and re-observed the dark bands. 

 On the other hand, no definite results regarding 

 the planet were obtained by the Lick observers 

 in 1889 and 1890. Measurements of the planet 

 by Young, Schiaparelli, Perrotin, and others 

 indicate a considerable polar compression. The 

 spectrum of the planet has been studied by 

 Secchi, Huggins, Vogel, Keeler, Slipher, and 

 others. The spectrum shows six bands of 

 original absorption, a line of hydrogen, which, 

 says Miss Clerke, " implies accordingly the 

 presence of free hydrogen in the Uranian atmo- 

 sphere, where a temperature must thus prevail 

 sufficiently high to reduce water to its con- 

 stituent elements." From a photographic study 

 of the spectrum at the Lowell Observatory in 

 1904, Slipher observed a line corresponding to 

 that of helium, indicating the presence of that 

 element in the planet's atmosphere. 



Herschel left our knowledge of the Uranian 

 satellites in a very uncertain state. The two 



