176 



PROCEEDINGS OF THE AMERICAN ACADEMY 



and may, consequently, conceal a narrow portion of the dark line. The 

 assumption of such an hypothesis seems to be fully supported by the 

 observations, as will be shown hereafter. It is furthermore to bo 

 remarked, that the outside margin of the ring C has always appeared 

 to me to be more sharply defined on that part of the ellipse fiirther 

 from the observer than on the side nearest. The case is the same for 

 the outer border of the ring A^ which appears sharper on its northern 

 than on its southern side. In both cases, the northern portion of the 

 ellipse is limited by the matter composing the surfiice of the rings 

 on their flat and illuminated side; while for the southern portion 

 it is seen a little edgeways, and this may account for the vagueness 

 of its outlines on this side. 



Soon after the beginning of my observations, in October, 1872, my 

 attention was called to a singular appearance not heretofore noticed, 

 as far as I am aware. Two small, dark, angular forms, r, Fig. 1, were 

 seen near the summit of the principal division of the rings on the fol- 

 lowing side, and apparently projected upon the ring B. After an 

 interval of three hours, no sensible change could be detected in the 

 position of these forms ; and on the following day they were seen 



Fig. 2. 



occupying about the same position. This phenomenon could easily be 

 explained by supposing there were some sort .of protuberances on the 

 external edge of the ring C, casting their shadow under the oblique 

 rays of the sun, which occupied then a proper position to answer to this 



