1891. ] Orbit of the Comes of Sirius. 4l 
either orbit. When the pair opens out in 1896 an orbit will be 
obtained that will be worthy of more reliance than any yet computed. 
In this paper most of the detailed working is left out, and only 
the more important steps given. 
II.—ConstTRUCTION OF APPARENT ELLIPSE. 
After all markedly erroneous measures have been set aside the 
observations of each year are combined. In the case of Sirius the 
following mean places were thus obtained : 
Position Angle. Distance. 
1862°22 84°72 10°25 
1863°18 80°95 10°42 
1864°22 79°60 10°92 
1865°23 77°06 10°73 
1866°23 74°68 10°60 
1867-23 12:27 10 98 
1868°25 70°63 11°15 
1869-20 68°76 11°17 
1871°22 64°15 10°92 
1872°21 61:29 11°28 
1873°22 60°84 10°57 
1874:14 58°03 IMsey, 
1875-21 56°68 11:10 
1970-21 53°11 Wels 
1877-98 52°24 10°77 
1879-40 48°60 10°36 
1880°14 48°95 3:99 
1881-18 45°05 10°05 
1882°13 42°85 — 9°58 
1883°15 39°79 9°36 
1884°18 36°59 8°82 
1885°20 33°87 8:02 
1886°14 20° 4ted 7°35 
1887°14 24-39 6°79 
1888-97 
These measures are then plotted down, and the interpolating curve 
drawn with as much care as possible. This curve ought to be a 
-segment-of an ellipse. 
The centre is found by the property of the ellipse that if tangents 
‘be drawn at the extremities of any chord the line passing through the 
