456 R. W. McFarland—Eccmtricity in the Earth's orbit. 



III. That the thickness of the system of rings is increasing 

 from the inner margin of the dusky ring to the outer border of 

 the ring C, as proved by the form of the shadow of the planet 

 thrown upon the rings. 



TV. That the cloud-forms seen near the outer border of the 



ring C attain diflferent heights, and change their relati^ 

 either by the rotation of the rings upon an axis, ( 

 local cause ; as indicated by the rapid changes in the indenta- 



'C 



tion of the shadow of the pla 



y. That the inner portion of the dusky ring disappears in 

 the light of the planet at that part which is projected upon its 

 disk. 



YI. That the planet is less luminous near its limb than in 

 the more central parts, the light diminishing gradually in ap- 

 proaching the border. 



VII. That the dusky ring is not transparent throughout, con- 

 trary to all the observations made hitherto ; and that it grows 

 more dense as it recedes from the planet ; so that, at about the 

 middle of its width, the limb of the planet ceases entirely to be 

 seen through it 



VIII. And, finally, that the matter composing the dusky 

 ring is agglomerated here and there into small masses, which 

 almost totally prevent the light of the planet from reaching the 

 eye of the observer. 



Art. LIX.— Curve of Eccentricity of the Earth's orbit; R W. 

 McFarland. 



tricity as found in Croll's work, and also in Stockwell's 

 former was computed with a view of explaming the clii 

 past time; the latter, in examining the moon's mean luuii^y- 

 It will be seen that the curves have the same general form, dif 

 fering in the value of the ordinates, more than in the position 

 of the maximum and minimum points. I have recomputed 

 the values by Le Verrier's old formulae, and find Croll's figures 

 correct in most cases, and not in error to the amount ol "OOl 

 except in one instance. My work extends over 1,100,000 years, 

 and is for points nearer together than Croll's. Stockwellsis 

 doubtless nearer correct than the other, but there is substantial 

 agreement. The two curves for the last 40,000 years, and tor 

 the next 30,000, are almost identical ; so nearly is this the case, 

 that only one line is drawn in the figure for those periods. 



