VOL. VI.] PHILOSOPHICAL TRANSACTIONS. 637 



appeared greatest in its first situation, it appeared least in this, because it was 

 almost in a circle that passed through the centre of the sun, whose equal arches 

 are by so much the more oblique, by how much they approach more to the limb 

 of his disk, and consequently appear less, according to the rules of optics; 

 mean time the diameter, that was turned from south to north, apparently kept 

 the same bigness it had near the centre, because it was in a circle almost parallel 

 to the horizon of the sun, which formed the representation of its limb, and 

 whose equal arches, by the same optical reasons, do not appear contracted.. 



Observations concerning Saturn, made in the same Place ivith the 



former. N" 78, p. 3024. 



At the same time that the new spots of the sun began to appear, Signor 

 Cassini observed in Saturn also something remarkable in regard of the unex- 

 pected change of his figure. Astronomers know, that this planet is for the 

 most part seen with arms or anses, fastened to the two sides of his disk, when 

 he is observed with some large telescope; and that he gains his round figure 

 only every 15 th year. This change was to come to pass this present year, and 

 Saturn to appear in that round figure, without his anses or handles, according 

 to the hypothesis and predictions of M. Huygens, published An. 1659; which 

 indeed has so happened, but not just within the time he had appointed; for 

 this spherical figure of Saturn should not have appeared, according to his suppo- 

 sitions, but in the month of July and August, and so continued for the rest of 

 the time that Saturn was to be visible at this time, and even for a part of his 

 appearance in the next year; but this roundness has been perceived sooner, and 

 Saturn has appeared orbicular since the end of May, at a time when he was dis- 

 tant enough from the sun and the horizon to be well observed ; and he has re- 

 mained in this figure to the llth of August. Signor Cassini then observed 

 him thus; but three days after he saw him with arms, though very narrow ones, 

 which still continue.* They are represented in pi. 14, fig. 12. 



Extract of two Letters from M. Hefelius, of June 19 and Oct. J, IGJI, 

 concerning several Celestial PhcBnomena. Translated from the Latin. 

 N" 78, p. 3027. 

 These communications contain some of Hevelius's late celestial observations ; 



* Mr, Huygens ascribes their being able to perceive the anses, though very narrow, to the long and 

 powerful telescopes used in these observations ; for that, with the former short ones, the edge of the 

 ring would not be visible. So tliat his prediction of the planet's appearance, according to his hypo- 

 tliesis, is not in the least discredited. 



VOL. I. 4 O 



