584 BIBLIOGRAPHY OF HERSCHEL^S WRITINGS, 



Herschel, W.: Synopsis of the Wpaxixcs or — Continued. 



Table of measures of Castor and comparison of calculated and oLserved 



angles. 

 An observation of Bradley's on Castor (1759) quoted. 

 New table of calculated and observed angles, including Bradley's 

 observations. The arc 45° 39' has been described in 43 years 142 

 days. 

 355 The regularity of tbe motions gives us reason to conclude that the 

 orbits of these stars are circular and at right angles to the line of 

 sight; if this be nearly true the time of a revolution will be about 

 342 years and 2 months. 

 366-372 y Leonis. [This case considered as before.] 

 372 Table of observations : the jieriod is about 1,200 years. 

 372 e Bootis. 

 378 ? HercuVis. 



380 d Serpen tis. 



381 ;k Virginis. 



382-3 Plates VII and VIII— figures of orbits. 



1804 94 353 Continuation of an Account of the Changes that have happened in the 



relative situation of douhle Stars. By William Herschel, LL. D., 

 F. R. S. Read Jmio 7, 1804. 



353 In my former paper {Phil. Trans., 1803, p. 339) I gave the changes in 

 the situation of six double stars. 



3.53 I used the best observations I had of the position of Castor, but as 

 the proper motions of 36 i^rincipal stars published in the Green- 

 wich observations give the motion of this star different from what 

 I used, it will be necessary to revieAv the arguments in the same 

 order as in the i)recediug paper. 



358 [The former conclusions in regard to Castor are confirmed.] 



359 In the further list of 50 double stars here given, 28 have undergone 



only moderate changes, less than 10°. 

 Thirteen have altered their situation above 10° but less than 20° ; 3 

 stars have changed more than 20° ; the six remaining have changed 

 between 30° and 130°. 

 359-384 [The various pairs considered and observations given. ] 



360 I have no longer supposed the solar motion to be directed to X Her- 



citlis^ but to a point at no very great distance from this star. 



1805 95 31 Experiments for ascertaining how far Telescopes ivill enahle «s to deter- 



mine very small Angles, and to distinguish the real from the spurious 

 Diameters of celestial and terrestial Objects; with an A2)j)licatio7i of the 

 Eesult of these Experiments to a Series of Observations on the Nature 

 and Magnitude of Mr. Hardixg's latel}/ discovired Star. [Jmko.] By 

 William Herschel, LL. D., F. R. S. Read December 6, 1804. 



31 "We know that a very thin line may be perceived and that objects 



may be seen when they subtend a very small angle ; but the case I 

 wanted to determine relates to a visible disk, a round, well-defined 

 appearance, which we may without hesitation affirm to be circular, 

 if not spherical." 

 [In 1774 Herschel found that a square area could not be distinguished 

 from an equal circular one till the diameter of the latter came to 

 subtend an angle of 2' 17".] 



32 1st Experiment, with the Heads of Pins. 



