152 Observations o?i the Figure of the Planet Saturn. 



equator of Saturn is much greater than it is on Jupiter, but 

 the curvature at the latitude of from 40 to 48" on Jupiter is 

 less than on Saturn. 



T repeated these ahernate observations many tifnes, and 

 the oftener I compared the two planets together, the more 

 striking was their different structure. 



May 26. 10-fect reflector. With a parallel thread mi- 

 crometer and a magnil'ying power of 400, I took two mea- 

 sures of the diameter of the points of greatest curvature. A 

 mean of them gave 6l,3 divisions = 1 \",[)S. After this, 

 T took also two measures of the equatorial diameter, and a 

 mean of them gave 60,5 divisions = 1 1'',27 ; but the equa- 

 torial measures are probably too small. 



To judge by a view of the planet, I should suppose the 

 latitude of the greatest curvature to be less than 45 degrees. 

 The eye will also distinguish the difference in the three dia- 

 meters of Saturn. That which passes through the points 

 of the greatest curvature is the largest ; the equatorial the 

 next, and the polar diameter is the smallest. 



May 27. The evening being verv favourable, I took 

 again two measures of the diameter between the points of 

 greatest curvature, a mean of which was 63,8 divisions 

 = 11'', 88. Two measures of the equatorial diameter gave 

 6) ,3 divisions = 1 1",44. 



June 1. It occurred to me that a more accurate measure 

 might be had of the latitude in which the greatest curvature 

 takes place, by setting the tixed thread of the micrometer 

 to the direction of the ring of Saturn, which may be done 

 with great accuracy. The two following measures were 

 taken in this manner, and are more satisfactory than I had 

 taken before. The first gave the latitude of the south-pre- 

 ceding point of greatest curvature 43° 26'; and the second 

 43" 1 3'. A mean of the two will be 43° 20'. 



June 2. I viewed Jupiter and Saturn alternately with a 

 magnifying power of only 300, that the convexity of the 

 eye-glass might occasion no deception, and found the form 

 of the two planets to differ in the manner that has been 

 described. 



With 200 I saw the difference very plainly ; and even 

 with 160 it was sufficiently visible to admit of no doubt. 

 These low po\4/ers show the figure of the planets perfectly 

 well, for as the field of view is enlarged, and the motion of 

 the objects in passing it lessened, we are more at liberty to 

 fix our attention upon them. 



I compared the telescopic appearance of Saturn with a 

 figure drawn by the measures I have taken, combined with 



the 



