650 



1'HII.OSOPHTCAL TRANSACTIONS. 



[ 



ANNO 1785. 



Intervals be- 

 tween the 

 observa- 

 tions. 



Numb, of pe 

 riods in ditto. 



Length of a 



single period. 



d 

 28 



h 

 15 



4 each of 



The stars to which » Antinoi was compared are in order thus : $ Aquilae 3d 

 magnitude, (3 Aquilae and 9 Serpentis 4th magnitude, i Antinoi 4th or 5th mag- 

 nitude, and f* Aquilae a bright 5th. I find, by several years observation, that 

 P Aquilae retains the same brightness, i Antinoi, which has been examined with 

 particular attention by Mr. Goodricke and myself, is suspected by us both to be 

 subject to a small variation, but not so apparent as to affect materially these com- 

 parisons, and possibly it may be only the effect of some optical illusion; for I 

 have frequently remarked, that both in the twilight and moon-light, or when 

 the air is in the least hazy, there is a greater difference between the brightness of 

 many of the stars, than in a dark night and clear sky. Mr. P. then gives a 

 journal of the comparisons with those stars, from July 17 till Dec. 4. And 

 then proceeds : In order to ob 

 tain a point of comparison 

 settling the periodical changes of its least and great 

 r Antinoi, which I suppose to be 

 constant, it is natural to fix on 

 that phasis which can be deter- 

 mined with the greatest precision ; 

 and this seems to be at the time 

 when it is between its least and 

 greatest brightness, as almost the 

 whole increase of brightness is 

 completed in less than 24 hours, 

 though the perfect completion is 

 performed only in 36 + hours ; 

 thus having settled this necessary 

 point, and found roughly the 

 length of a single period, the 

 computations, in order to obtain 

 greater exactness, are as annexed. 



Perhaps other astronomers may not exactly agree with me, in fixing the times 

 as set down in the first column ; for my part, I determined them without paying 

 any regard to the results, by taking a medium between the times when » Anti- 

 noi had rather passed its least brightness, being nearly equal to i Antinoi, and 

 when it was a little, but undoubtedly, brighter than (3 Aquilae. Though it does 

 not appear, as already said, that any of the other phases can be settled with 

 equal precision, yet different comparisons may prove satisfactory towards 



Time when i An- 

 tinoi was between 



est brightness. 



1784 h 

 Sept. 12, at 20 ( 

 Oct 11, at 11 \ 

 Sept. 12, at 20 > 

 Oct. 18, at 20 J 

 Sept. 12, at 20 \ 



36 



43 



64, 12 



9 



29 



30" 







Oct. 26, at 00 

 Sept. 12, at 201 

 Nov. 16", at 8 J 

 Sept. 19, at 20 1 

 Oct. 1 8, at 20 J 

 Sept. 19, at 20 

 Oct. 26, at 00 

 Sept. 19, at 20 

 Nov. 1 6, at 8 J 

 Oct. 11, at 11 

 Nov. 16, at 

 Oct. 18, at2( 

 Nov. l6, at 



Length of a single period, on a mean, 



57 12 



35 21 



28 12 



6 



h 

 3| 



4| + 



41- 



4 

 6 



5| + 



*1 



44- 



3 

 4 30 



