2GS THE NEBULAR HYPOTHESIS. 



the outer rims may not have greater absolute velocities; 

 and thus the resulting planets may have retrograde rota 

 tions. Again, the sectional form of the ring is a circum 

 stance of moment ; and this form must have differed more 

 or less in every case. To make this clear, some illustra 

 tion will be necessary. Suppose we take an orange, and 

 assuming the marks of the stalk and the calyx to represent 

 the poles, cut off round the line of the equator a strip of 

 pec l. This strip of peel, if placed on the table with ita 

 ends meeting, will make a ring shaped like the hoop of a 

 barrel a ring whose thickness in the line of its diameter 

 is very small, but whose width in a direction perpendicular 

 to its diameter is considerable. .Suppose, no\v, that in 

 place of an orange, which is a spheroid of very slight 

 oblateucss, we take a spheroid of very great oblatenes?, 

 shaped somewhat like a lens of small convexity. If from 

 the edge or equator of this lens-shaped spheroid, a ring of 

 moderate si/e were cut off, it would be unlike the previous 

 ring in this respect, that its greatest thickness would be in 

 the line of its diameter, and not in a line at right angles 

 to its diameter: it would be a ring shaped somewhat 

 like a quoit, only far more slender. That is to say, ac 

 cording to the oblateness of a rotating spheroid, the de 

 tached ring maybe either a hoop shaped ring or a quoit- 

 shaped ring. 



One further fact must be noted. In a much -flattened 

 or lens-shaped spheroid, the form of the ring will vary with 

 its bulk. A very slender ring, taking off just the equatorial 

 surface, will be hoop-shaped ; while a tolerably massive, 

 ring, trenching appreciably on the diameter of the spheroid, 

 will be quoit-shaped. Thus, then, according to the oblate- 

 ness of the spheroid and the bulkiness of the detached ring, 

 will the greatest thickness of that ring be in the direction 

 of its plane, or in a direction perpendicular to its plane. 

 But this circumstance must greatly affect the rotation of 



