VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. J 03 



any perceptible change ; 28 + days decreasing from the middle of its full bright- 

 ness to the middle of its least ; and 35 + increasing from the middle of its least 

 brightness to the middle of its full. These results being deduced from only the few 

 observations I have made, cannot of course be very accurate, but may easily and 

 soon be corrected by comparing any future observation with those communicated in 

 this paper. 



From the observations in the journal the periodical changes were deduced as fol- 

 lows : The length of a single period of 6/ days, being first settled, from a succession 

 of observations between March and May, and of 69 between April and June, we 

 may proceed to obtain a greater exactness from dates, thus : 



Middle of its greatest brightness. Days. 



I70f)' J ° 18 J * nterva l °f 4 periods, making the length of a single one 65| 



17Q^ A° '1 10 J I nterva * °f 3 periods, making the length of a single one 6*4 



Middle of its least brightness. 



1706* Mav 10 J * nterva l °f 3 periods, making the length of a single one 6*2 



1796' March 4 } Interval of 2 periods, making the length of a single one 59\ 



A single period, on a mean 623 



Had it been requisite to have given any preference to one of these 4 results, I 

 should have chosen the 3d ; not only on account of the exactness of the observa- 

 tions themselves, but particularly because the changes when near its least bright- 

 ness are quicker ; however, they all agree more satisfactorily than I think could be 

 expected ; still it must be remembered, that the mean period here determined is 

 merely for this set of observations, it being yet unknown what kind of irregularities 

 it is liable to ; for while I am now writing, in the month of August, its changes 

 seem different from those of the preceding 4 periods ; and how these perturbations 

 will terminate, cannot be settled in the present account, as I mean here to con- 

 clude it. 



The other variable that I have discovered is, as already mentioned, in the North- 

 ern Crown. Its right ascension is 235°2 / 51 // , and declination 28° 4Q'±. This 

 star, though not in Flamsteed's catalogue, is marked on Bayer's maps of the 6th 

 magnitude. Several years ago, in 1783, 1784, and 1785, I suspected it to be 

 changeable, which induced me to make the memorandums here copied in the 

 journal, since which time I have often seen it, but not perceiving any alteration, 

 the dates were neglected till the spring of 1795 ; I then had the satisfaction of find- 

 ing my suspicions confirmed, it being invisible ; but on the 20th of June, it ap- 

 peared of the 9.10th magnitude, and went through its various changes as follows: 

 in 6 weeks it had increased to its full brightness, the middle time of which was 

 August 1 1th, 1795. At its full brightness it was of the 6.7th magnitude, and re- 

 mained the same without any perceptible alteration for about 3 weeks : it then was 

 3-|- weeks in decreasing to the 9.10th magnitude, and disappeared a few days after. 



