OF ARTS AND SCIENCES. 177 



hypothesis. But, some days later, another of these singular forms was 

 observed 180° from the first, on the preceding side, ats. This at once 

 overthrew the supposition that they were shadows cast by protuber- 

 ances existing on the ring G ; since in this case the shadows would 

 have been projected opposite the sun on the ring (7, and not on the ring 

 B. Since that time, I have rarely observed the planet without seeing 

 some of these singular appearances, either on one side or the other, but 

 generally on both sides. The number of these dark forms is variable. 

 One, two, three, four, and even five, have been seen at the same moment, 

 and on the same side. Though these forms are variable, and appear 

 and disappear, I have never been able to detect in one night any 

 change of position which could be ascribed to the rotation of the 

 rings. 



The most plausible explanation of the phenomenon which I can con- 

 ceive is, that the inner margin of the ring B, which forms the outer 

 limit of the principal division, is irregular, jagged, and deeply indented, 

 as shown at A, Fig. 2, which represents Saturn as it would appear to 

 an observer placed above one of its poles. 



As Bond speaks of the principal division of the rings as " not being 

 perfectly elliptical," and as in one instance he has suspected that it 

 " was narrower in some places," it is to be inferred that he had some 

 faint glimpses of the phenomenon which I have observed, and which 

 possibly may be more conspicuous now than twenty years ago. 



But the fact that this phenomenon has not been observed earlier 

 does not necessarily prove that it had no existence before ; as it is well 

 known, by those who have had experience with the telescope, that one 

 may look for a long while at a celestial object, and miss perceiving 

 what he will readily see when once he is told where to look, and what 

 to look for. Seeing what is new and unsuspected is quite different 

 from seeing what has been observed before. 



Though no noticeable changes in the position of the dark angular 

 forms C(juld be observed in the course of two or three hours, it does not 

 follow that the system of rings does not rotate upon an axis, as theory 

 indicates ; since the supposed indentations seen on the ansae would bo 

 placed in the most unfavorable position for showing their motion, if 

 they have any, because it would be accomplished almost in a line with 

 the visual ray, either approaching or receding from the observer. 



Next to this division, but much less conspicuous, and to be seen only 

 on very good nights, is a narrow, grayish, and somewhat diffused line, 

 called " the pencil line," shown at b, Fig. 1. I have never been able 

 to trace this line all around the planet, as it diminishes very rapidly 



VOL. XI. (N. S. III.) 12 



