36. 



NOTE ON WILLIAM BALL'S OBSERVATIONS OF SATURN. 



[From the Monthly Notices of the Royal Astronomical Society, Vol. XLIII. (1883).] 



IN No. 9 of Vol. I. of the Philosophical Transactions, a brief account 

 is given of an observation of Saturn made on Oct. 13, 1665, at 6 o'clock, 

 by William Ball, at Mamhead, near Exeter, and it is suggested that the 

 appearance presented by the planet may perhaps be caused by its being 

 surrounded by two rings instead of one. 



This account has recently given rise to considerable discussion ; and 

 there are some difficulties connected with it which do not appear to have 

 been satisfactorily cleared up. In a few copies of the volume this account 

 is illustrated by a figure, in which the external boundary of the ring, 

 instead of being of a regular elliptical form, has two blunt notches or 

 indentations at the extremities of the minor axis. The plate containing 

 this figure, however, is wanting in by far the larger number of the copies. 



Now, I think, it may be safely asserted that no telescope, capable of 

 shewing Saturn's ring at all, ever exhibited it in this extraordinary form, 

 and therefore if the above figure faithfully represents William Ball's drawing, 

 he was either a very inaccurate and careless observer, or he must have 

 been provided with very inadequate instrumental means. 



On the other hand, we have ample proof that he was a careful and 

 assiduous observer, that in particular he made a long series of observa- 

 tions of Saturn, and that these were made with instruments not much 

 inferior to those employed by Huyghens himself in similar observations. 



