S92 PLANET SATURN. 



poles a Utile more extended on botli sides toward Ihi 

 equatorial parts. It is in consequence of the increase of 

 the length of this flattening, or from some other cause, 

 that a somewhat greater curvature in the latitudes of 40 

 or 45 degrees north and south has taken place ; and as 

 these diflerenceis are very minute, it will not appear ex- 

 traordinary that they should have been overlooked in 

 1789, when my attention was entirely taken up with an 

 examination of the two principal diameters of thp 

 planet. 

 Onmagnlfybg The use of various magnifying powers in observing 

 powers, parti- minute objects is not generally understood. A low 



cularlylow power, such as 200 or 160, with which I have seen the 

 powers. ^ ' . 



figure of Saturn, is not suflicient to show it to one who 



has not already seen it perfectly well with an adequate 

 high power ; an observer, therefore, who has not an in- 

 strument that will bear a very distinct magnifying power 

 of 500, ought not to expect to see the outlines of Saturn 

 so sharp and well defined as to have a right conception 

 of its figure. The quintuple belt is generally a very good 

 criterion : for if that cannot be seen, the telescope is not 

 sufficient for the purpose; but when we hare entirely 

 ij i convinced ourselves of the reality of the phenomena I 

 have pointed out, we may then gradually lower the pow^ 

 er, in order to be assured that the great curvature of the 

 eye-glasses giving these high powers, has not occasioned 

 any deceptions in the figure to be investigated, and this 

 was the only reason w^hy I mentioned that I had also seen 

 the remarkable figure of Saturn with low powers. 

 I'hc figure of ^ y^^Y ^^^^^^^^ ^^^es it becomes necessary to calculatd 

 Saturn was not every cause of an appearance that falls under the pro- 



attc-cted by yince of mathematical investigation. For this reason I 

 gibbosity. ° 



have always looked upon an astronomical observation 



without a date as imperfect, and the journal-method of 



communicating them is undoubtedly what ought to be - 



used. For instance, w hen it is known that my last year's 



most decisive observation, relating to the singular figure 



of Saturn, was made the 5th of May, astronomers may 



then calculate by this date the place of Saturn and of 



the earth ; their distances from each other, and the angle 



of illumination of the Saturnian disk; by these means 



