OF ARTS AND SCIENCES. 191 



XIII. 



ON SATURN'S RINGS. 

 By L. Trouvelot. 



Presented Nov. 14th, 3877. 



In No. 2146 of the " Astronomische Nachrichten," Professor Asaph 

 Hall, in giving the results of his observations on the planet Saturn, 

 makes some remarks on my observations of the same planet which 

 were published in the Proceedings of the American Academy for 

 the year 1875-1876. 



Professor Hall began his observations in June, 1875. "At first," he 

 says, " my attention was not sijecially given to the appearance of the 

 Ring. . . . After the picture of Saturn was made by Mr. L. Trouve- 

 lot with our telescope in September, 1875, I gave more attention to 

 the appearance of the Ring, and I have done so during the last year. 

 . . . On account of the confidence I have in the drawings made by so 

 skilful an artist, I have been surprised to find that I have never been 

 able to see the slightest trace of two phenomena of the Ring which 

 Mr. Trouvelot draws with the greatest distinctness." 



Here Professor Hall refers : first, to the notch which I have repre- 

 sented in the shadow of the globe of Saturn on the Ring ; second, to the 

 jagged or tooth-like appearance of the principal division on the ansae. 



Had Professor Hall consulted his memory, undoubtedly his surprise 

 would have been less ; since he would have remembered that on the 

 same drawing to which he refers, and which I made at the Naval 

 Observatory in his presence, I represented the shadow of the Ball with 

 its convexity turned towards the planet, just as he saw it later and 

 described it, and as indeed I continued to see it during 1876. Know- 

 ing that the shadow was curved inward in September and not notched, 

 I fail to understand why he should have expected to see a notched 

 shadow rather than a curved one, when almost a year had elapsed 

 between his observations and mine, in December, 1874. 



Besides myself, Schroter, Lassell, De La Rue, Jacob, Bond, Coolidge, 

 Tuttle, and many others, have seen the shadow more or less notched. 



