visible from d to e, as the bright light of the planet would shine 

 through in its place, and be undistinguishable from that of the 

 rings. It may be objected that the invisibility of the planet 

 through the principal division is due to the thickness of the ring 

 G; but in this case, why should the black sky be seen, if the 

 planet is invisible? 



Besides the two dark gaps or divisions of which I have just 

 spoken, the rings are subdivided by concentric zones or belts, 

 which reflect light of different hues and intensity. Though only 

 three of these belts are conspicuous, I have found by careful ex- 

 amination that there are six which I can always recognize when- 

 ever the illumination is good, and the image steady. These 

 zones are represented on the diagram, fig. 1, at A, B, 0, Z>, E, F. 

 On several occasions, I have had a pretty distinct impression of 

 seeing the whole surface, from C to E inclusive, grooved, as it 

 were, by numerous narrow concentric belts. These impressions 

 may have been illusory, as they were almost instantaneous ; but 

 I have since learned by experience, that, after all, rapid impres- 

 sions are not so much to be discarded, as, quite often, even 

 more fugitive impressions have proved in the end to be real. 

 A striking instance in my own experience may be worth record- 

 ing. This summer I made a study of the Horseshoe Nebula in 

 Sagittarius with my B-J-inch refractor. During the course of my 

 observations, I was much annoyed by what appeared to me as 

 faint ghost-like reticulated shadows projected upon the nebula. 

 I at first thought I had left the reticule of squares mled on glass 

 in the eye-piece ; but having convinced myself that this was not 

 and the same appearance again presenting itself, I wiped my 

 I, but with no better result. As I experienced the same 

 ng on other nights, I paid no more attention to it, thinking 

 the trouble was in my sight. Some time afterwards, while in 

 Washington, I had an opportunity of studying the same nebula 

 with the great twenty-six inch refractor of the Naval Observa- 

 tory. I was not a little surprised to see that the ghost-like ret- 

 icule which I wanted so much to rub out of my eye while at 

 home, was caused by dark channels in the nebula itself, which 

 is divided on the preceding side by bright luminous patches, 

 separated by dark intervals. 



In order of brightness, the zones or belts composing the sys- 

 tem of rings run as follows : (7, D, B, E, A, F; C being by far 

 the brightest, and F by far the darkest. The zones A and B 

 bave a bluish cast, or light slate color ; C7 is of a bright luminous 

 white; D is slightly gravish ; ^ is a little darker; while j; 

 which is very dark, is tinged with bluish purple. 



A is separated from B by the pencil line; B from C by the 

 principal division : while the others do not show any separation 

 whatever, and are only limited by the contract of thuir different 



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