Gore — A Catalogue of Binary Stars, 8fc. 595 
Assuming a parallax of 0"'45 Peter's "final" orbit (period = 782*6 
years) gives for the combined mass of tbe components 0*461 (sun's 
mass =1), and a mean distance of 65*62 times the sun's mean distance 
from the eartb. This orbit was used by me in computing the relative 
brilliancy given in the Catalogue. 
55. S Equuleii = O 5 535. This is the brighter component of the 
wide double star 5 2777. It has the shortest period of any known 
binary, three revolutions having been completed since its discovery in 
1852. The period found by Wrublewsky is probably not far from the 
truth, but his orbit does not represent the measures very satisfactorily. 
Some recent measures are : — 
1883*55 : 307°*6 : 0''-21, Eurnham. 
1887*88 ; 203*2 : 0 -47, Schiaparelli. 
1888*60 : 213 -4 : 0 -35, Leavenworth. 
1888*69 : 189 *9 : 0 '25, Eurnham. 
Eurnham says (^,iV., 2957) — ''1889*515, slight elongation with 
the 36-inch in the direction of 343°*2. Distance not more than 0"*10." 
56. T Cygni = A. Clark, 13. Eecent measures show that my orbit 
will require revision. 
Some of these measures are : — 
57. ^ Aquarii = ^ 2909. An arc of only about 53° of the apparent 
orbit has been described since its discovery by Sir W. Herschel in 
1779. The period found by Doberck is the longest yet computed for 
any binary star. 
Some recent measures are : — 
1880*78 : 
1888*733 : 
1370.4 . l/^Q4^ Frisby. 
" Single, with all powers 1 
to 3300. Good definition 
36°-5 : 0"*50, Eurnham. 
1889*49 
1885*720 : 328°*0 : 3"'330, Perrotin. 
1886*945 : 326 -53 : 3 *43, Tarrant (^.iV., 2866). 
1888*93 : 325 *8 : 3 *08, Leavenworth (6 nights). 
58. TT Cephei = O ^ 489. About 40° of the apparent orbit has 
been described since 1846. Glasenapp's elements represent the 
measures closely. 
