discovered z Ophiuchi in I 783, and the elements of the orbit depend still on the angle, which he then measured. His observation appears to be allright although the components were probably only half a second of arc asunder (for every degree his angle is wrong the period will have to be altered nearly a year), but in 1802 and 1804 he thought that he glimpsed the companion to the north of the main star, and that cannot possibly have been the case. It would indicate a period of revolution of

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... e star from 1825 till 1837, and as his observations are usually very accurate, a normal place was formed for 1836.67 from his best measurements. I have done my best to represent that position together with the modern observations, but have failed to do so. The components were only a fraction of a second asunder, and the star does not rise above 24O over the horizon at Dorpat, so it is no wonder that the observations made with the 9-inch refractor are affected by large constant errors. Some of the orbits upwards of 300 years, and an orbit which would not satisfy the accurate modern measures. W. Struve observed this calculated are -as filows: E l e m e n t s I I1 I11 0 = 7 I 0 2 l t 76O 12' 74O 26' Y = 66 39 66 4 68 52 e = 0.5339 0.5338 0.5052 P = 232.43 223.82 216.37 T = 1815.95 1814.79 I 820. I 5 a = 1'333 11,307 11349 rz = 1 7 I 8 1 7 45 25 35 O b s e r v a t i o n s t 40 Q O Ad AQ Ad d Q Ad