174 PROCEEDINGS OF THE AMERICAN ACADEMY 



IX. 



ON SOME PHYSICAL OBSERVATIONS OF THE 

 PLANET SATURN. 



Bt L. Trouvelot. 

 Read by William A. Rogers, Dec. 14, 1875. 



During the last four years I have had many occasions to observe 

 the planet Saturn, and to study its physical constitution under very 

 favorable circumstances. My series of observations extends over more 

 than a hundred nights, many of which were as good as could possibly 

 be desired, both for the steadiness of the image, and for the amount of 

 light. 



The observations on which this communication is based were made : 

 1". With the fifteen-inch refractor of the Harvard College Observatory, 

 while I was employed by Professor Winlock in making the sketches 

 for the series of the astronomical engravings published by him. By 

 his kind permission I have availed myself of considerable of the data 

 thus obtained. 2°. With the twenty-six-inch refractor of the Wash- 

 ington Observatory while it was still in the hands of Messrs. Alvan 

 Clark & Sons. 3°. With the six-and-one-quarter-inch refractor of my 

 own Physical Observatory at Cambridge. During the past summer, I 

 was honored with an invitation from Admiral C. H. Davis, Superin- 

 tendent of the Naval Observatory, to visit Washington and make some 

 sketches with the njagnificent instrument of this establishment. I thus 

 had an excellent opportunity to confirm all my previous observations. 

 The powers used ranged, according to the amount of light and the 

 steadiness of the atmosphere, from 140 to 700. On good nights, 

 however, higher powers have been tried, but never with advantage, as 

 the light lost by the use of high powers is generally of more impor- 

 tance for good vision than a superior enlargement with a reduced 

 amount of light. 



