454 L. Trovvelot — Physical Observations of tSaturn. 



1, and pass througli n ; while, on the contrary, it is seen above 



I was surprised, at first, bj this singular phenomenon ; but I 

 at last satisfied mjself with the following explanation : Tf we 

 conceive the dusky ring to be made up either of vapors or of 

 11 independent solid bodies, and, moreover, if we 

 I the thickness of this ring as increasing from its interior 

 margin to its outer limit, we shall have an easy explanation of 

 the observed phenomena. When the matter composing this 

 ring, whether solid or gaseous, is seen projected upon the disk 

 of the planet brilliantly illuminated, it will be lost, and will in- 

 dividually disappear, absorbed by the irradiation of the bright 

 light surrounding it, and it will remain visible only at that part 

 where it forms a stratum thick enough to overpower the effect 

 of irradiation. 



The fact that the distortion of the inner margin of the dusky 

 ring is not abrupt at m and p, where it enters upon the disk, 

 but is gradual, seems to prove that the planet is less luminous 

 on its border than elsewhere, providing the above explanation 

 holds good ; and this may be owing to the absorption caused 

 by an atmosphere surrounding the planet. 



Bond has represented the limb of the globe of Saturn as seen 

 through the whole width of the dusky ring. In this he agrees 

 with all previous observers. All the drawings of Saturn repre- 

 sent the limb of this planet as plainly and equally visible through- 

 out the dusky ring, becoming invisible only where it enters 

 under the internal margin of the ring M In Bond's memoir, 

 it is positively stated that Mr. Tuttle saw the limb of the planet 

 through the whole width of the dusky ring. If these observa- 

 tions are correct, — as without doubt they are, — the solid parti- 

 cles, vapors or gases, composing this ring, must have undergone 

 some changes of position since Bond's time ; as by using the 

 same instrument, and even one of almost double the aperture, 

 I have not been able to confirm these observations. 



During the last four years, I have never been able to see the 

 limb of the planet Saturn under the dusky ring, beyond the 

 middle of its width. As it enters under it at m and p, it re- 

 mains quite distinct for a short distance ; but, as it advances 

 farther in, it diminishes gradually ; and it entirely vanishes at 

 about the middle, at u and v; as if the matter composing the 

 dusky ring was more dense or thicker towards its outer border. 

 This observation has been so carefully made, and so many times 

 repeated, the phenomenon has been so distinctlv seen, that there 

 is not the least doubt in my mind as to its reality. Therefore 

 it seems pretty certain that changes have lately taken place in 

 the distribution of the matter composing the dusky ring. 



As already shown, the substance composing the dusky ring 



