OF ARTS AND SCIENCES. 



175 



NiinKM'ons obscrvors, amoii^ whom ixre such einiiioiit astroiiomors as 

 Sir AVilliaiu and Sir .Toliii Ihrsclu'l, Otto Struvi', Daws, lioiid, &,c., 

 have made careful studies of this phinct; and it is not, therefore, to he 

 expected that ver^' important (hscovcries remain to he made hy hiter 

 observers. As I have had the op[)ortunity 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 my admiration for the accuracy and fidelity of his 

 observations. 



The following diagram, representing the outlines of Saturn and its 

 rings, will facilitate my explanations, and give clearness to the sub- 

 ject : — 



Fig. 1. 



By looking at the rings, attention is at once attracted to a con- 

 spicuous dark line, apparently concentric with the outer margin of the 

 rings, and boldly surrounding the planet, and adorning it by its sharp 

 contrast. This dark line is known as " the principal division of the 

 rings," and is shown at a, Fig. 1. Owing to the effect of perspective, 

 it always appears widest at the two extremities of its major axis, on 

 that portion called " the ansae," as there only, it is seen without fore- 

 shortening. I have carefully compared the intensity of this dark line 

 with the sky outside of the rings, and inside of the ansje ; and I have 

 always found it to be slightly lighter. All my observations also agree 

 in showing this line as appearing a little narrower on the side farther 

 from the observer, at c, Fig. 1, than it appears on the opposite side, 

 at d. This phenomenon could readily be explained by supposing that 

 the outside margin of the ring (7 is on a plane higher than the ring B, 



