154 PHILOSOPHICAL TRANSACTIONS. [aNNO 1715. 



neck, to be of the 4th magnitude, and represented it by &, taking it for a fixed 

 star that constantly appears. 



The star next the head of the Svan, observed by Hevelius in 1670 and 1671, 

 gave M. Kirch the opportunity of finding the mutable appearance of the star y 

 in the Swan's neck. For when he was in hopes that the same star would appear 

 frequently, in the same manner as that other in the Whale's neck, which after 

 its first disappearing had appeared again presently after to Hevelius, he sought 

 for it on the first and 6th of July, 1686, O. S. both clear nights, but did not 

 find it; but rather found that the star of the 5th magnitude in the Swan's neck, 

 represented by Bayer by y^^ was wanting. Yet on the Qth of October, O. S. 

 he saw it very plainly with his naked eye. And because he thought that it 

 would again disappear to the naked eye, he delineated some small stars round 

 it, by means of a 2-foot telescope, that by comparing these with it, he might 

 compute its magnitude, when it should decrease, as represented by fig. 5, 

 plate 4. 



He found also that that star had gradually decreased, till he could not see it 

 through an 8-foot telescope ; though he could still observe that other star in 

 the Whale's neck through a 4-foot telescope. From that time he looked for 

 that star for several nights together, but to no purpose; but at length he found 

 it again on the 6th of August l687, O. S. with an 8-foot telescope, but ex- 

 ceedingly small. And from that time he found it daily increase more and more ; 

 so that on the 23d of October, O. S. it appeared again for the first time to the 

 naked eye, though still exceedingly small. On the 2d of November, O. S. it was 

 very visible, and even after the 26th of November, O. S. though this last day 

 it was decreasing again. Afterwards it could not be seen, but through a tele- 

 scope, and at length it became so small, that he could not observe it with an 

 8-foot telescope. And thus M. Kirch found at this time, that from one disap 

 pearing to another, there was about a year, a month and a week. The follow- 

 ing observations likewise showed that this star observed a pretty regular period 

 in its appearing, though not of an equal magnitude at any particular time: nay 

 it sometimes happened that it was quite invisible to the naked eye, though it 

 could be seen through a telescope, and had come to its greatest magnitude ; as 

 in the latter end of 1688, and beginning of 1689. O" the contrary, in J690 

 this star became more visible, and considerably larger than the neighbouring 

 star, which Bayer has placed without the Swan's neck, near;^, and represented 

 by no letter ; but M. Kirch marked it by ;|. And after the latter had often ob- 

 served the appearing and disappearing of this star, he found it to be very regular, 

 and to perform its revolution in 404 days and a half. 



This new star of M. Kirch's was observed at London about the 15th of July, 



