of the Planet Saturn. 131 



In order to have the testimony of all my instruments, on 

 the subject of the structure of the planet Saturn, I liad pre- 

 pared the 40-feet reflector for observing it in the meridian. 

 I used a magnifying power of 3<)0, and saw its form ex- 

 actly as I had seen it in the 10- and 20-fect instruments. 

 The planet is flattened at the poles, but the spheroid that 

 would arise from this flattening is modified by some other 

 cause, which I suppose to be the attraction of the ring. It 

 resembles a parallelogram, one side whereof is the equato- 

 rial, the other the polar diameter, with the four corners 

 rounded otf so as to leave both the equatorial and polar 

 regions flatter -than they would be in a regular spheroidical 

 figure. 



The planet Jupiter being by this time got up to a consi- 

 derable altitude, I viewed'it alternately with Saturn in the 

 10-feet reflector, with a power of 500. The outlines of the 

 •figure of Saturn are as described in the observation of the 

 40-feet telescope ; but those of Jupiter are such as to give 

 a greater curvature both to the polar and equatorial regions 

 than takes place at the poles or equator of Saturn which are 

 comparatively much flatter. 



May 12. I viewed Satiun and Jupiter alternately with 

 my large lO-fect telescope of 24 inches aperture : and saw 

 plainly^that the former planet differs much in figure from 

 the latter. 



The temperature of the air is so changeable that no large 

 mirror can act well. 



May 13. 10-fcet reflector, power 300. The shadows 

 of the ring upon the body, and of the body upon the ring, 

 are very black, and not of the dusky colour of the heavens 

 about ilie planet, or of the space between the ring and 

 planet, and bctvi'cen the two rings. The north-following 

 part of the ring, close to the planet, is as it were cut off" by 

 the shadow ot°the body: and the shadow of the ring lies 

 south of it, bni close to the projection of the ring. 



The planet is of the form described in the observation of 

 the 40-feet telescope ; I see it so distinctly that there can be 

 no doubt of it. By the appearance I should think the 

 points of the crcatest curvatui-c not to be so far north as 45 



A 



degrees. 



The evcnmg being very calm and clear, I took a measure 

 of their situation, which gives the latitude of the greatest 

 curvature 40" 2l'. A second nieasure gives 15" 41'. 



Jupiter being now at a considerable altitude, 1 have viewed 



it alternately with Saturn, The figure of the two planets is 



decidedly different. The flattening at the poks and on the 



K^ 4 ixjuator 



