L. TroHveht— Physical Ohse 



Art. JNITL—On some Physical Observations of the Planet Saturn ; 

 by L. Trouvelot.* 



During the last four years I have had many occasions to 

 observe the planet Saturn, and to study its physical constitu- 

 tion under very favorable circumstances. My series of obser- 

 vations 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 Col- 

 lege Observatory, while I was employed by Professor Winlock 

 in making the sketches for the series of the astronomical en- 

 gravings 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 Washington Observ- 

 atory 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 sum- 

 mer, I was honored with an invitation from Admiral C. H. Davis, 

 Superintendent of the Naval Observatory, to visit Washington 

 and make some sketches with the magnificent instrument of 

 this establishment I thus had an excellent opportunity to con- 

 firm all my previous observations. The powers used ranged, 

 according to the amount of light and the steadiness of the at- 

 mosphere, 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 importance 

 for good vision than a superior enlargement with a reduced 

 amount of light. 



Numerous observers, among whom are such eminent astron- 

 omers as Sir William and Sir John Herschel, OttoStruve, Dawes, 

 Bond, etc., have made careful studies of this planet ; and it is 

 not, therefore, to be expected that very important discoveries 

 remain to be made by later observers. As I have had the op- 

 portunity of observing with the same instrument many of the 

 celestial objects previously studied with so much success by 

 Professor George P. Bond,^ it gives me the greatest pleasure to 

 express mv admiration for the accuracy and fidelity of his ob- 

 servationsr 



The following diagram, representing the outlines of Saturn 

 and its rings, will facilitate my explanations, and give clearness 

 to the subject : — 

 * Read before the Amer. Acad, of Arts and Sciences by William A.. Rogers, 



