Professor Struve on Double and Triple Stars. 79 



Art. XI. — Report on Double Stars, from a Review of the 

 Starry Heavens made with the Great Achromatic Telescope 

 of Fraunhofer, addressed to Prince Lievex, Curator of 

 the University of Dorpat. By F. G. Struve, Director of 

 the Observatory. 



It was in the observatory of Dorpat that the observations of 

 Herschel on double stars were first repeated. Since the year 

 1820, (as will be found in the second volume of the Observa- 

 tions of Dorpat) I have endeavoured to prove that the com- 

 panions of the double stars g of the great Bear, and p of Ser- 

 pentarius, in whose relative position Herschel had remarked 

 the most considerable changes, had a circular motion round 

 the principal star. The former had described 227° of its circle 

 since 1781, and the latter 281° since 1779, from which it results 

 that the duration of their revolution is sixty and fifty years, 

 and consequently less than the revolution of the Georgium 

 Sidus round the sun. This motion of the stars round one 

 another is necessary, in order that two neighbouring stars which 

 mutually attract each other may not meet; and it demon- 

 strates without doubt that the fixed stars are subject to the 

 laws of gravitation, which the clusters of stars made us only 

 conjecture. It is very remarkable that the fixed stars whose 

 revolutions are known to us are among those whose proper 

 motions are \he greatest. 



These observations have been completely confirmed by the 

 measurements on the same subject taken in England by Mr Her- 

 schel Jun. and Mr South, and which are published in the Philo- 

 sophical Transactions forl825 and 1826. These measurements 

 include all the double stars already known (which I have col- 

 lected in a catalogue for the year 1820, published at the Ob- 

 servatory of Dorpat) and several stars newly discovered ; and 

 theypresenta series of observations which may be ranked among 

 the most remarkable of modern times. 



The motion of one fixed star round another ought to oc- 

 casion different phenomena. Herschel has lost sight of the 

 companions of several stars which previously he had distinctly 

 seen double. It is probable that the principal star covers the 



