CATALOGUE. ASTRONOMY, STARS. 



329 



Iterschel's second catalogue of double stars. 



Ph. tr. 1783. 40. 

 Herschel's 1000 new nebulae. Ph. tr. 178G. 



457. 

 Herschel's second thousand of new nebulae. 



Ph.tr. 1789. 212. 

 Herschelon nebulous stars. Ph.tr. 1791-71. 



Stars surrounded by a faint light, which Dr. Herschcl 

 thinks must be a shining fluid. 



Herschel. Ph.tr. 17<)5.46. 



Found 600 stars in a circle 15' in diameter. This state- 

 ment has been much mistaken by some authors. 



Herschel's 500 new nebulae. Ph.tr. 1802. 



477. 

 Herschel on the changes of double stars. Ph. 



tr. 1803. 339. 1804. 353. Nich. VII. 210. 

 Cassini's verification of Herschel's double 



stars. A. P. 1784. 33 i. 



Asks if they are satellites. Differs a little from Herschel 

 respecting the colour of the stars. 



Michell. Ph. tr. 1784. 35. 



Conjectures that some stars revolve round others. 

 Lenionnier on the nebula in cancer. A. P. 



1789.610. 



A catalogue of the stars. The double star zeta lyrae some- 

 times appears accompanied by several little stars. 



Account of Dr. Herschel's paper on llie changes thai 

 have happened, during the last twenty five years, in the 

 fetative situation of double stars ; tcith an investigation 

 of the cause to which they are owing. From the Juur- 

 ' vals of the Royal Institution. II. 

 Dr. Herschel devotes this paper principally to the con- 

 sideration of the second class of the systems into which he 

 has divided the sidereal world. After cursorily remarking, 

 with respect to the solar system, as a specimen of the first 

 class, which, among the insulated stars, comprehends the 

 sun, that the affections of the newly discovered celestial 

 bodies extend our knowledge Of the construction of this 

 insulated system, which is best known to us ; he proceeds 

 to support, by the evidence of observation, the opinion, 

 which he has before advanced, of the existence of binary 

 sidereal combinations, revolving round the conimon centre 

 of gravity. Dr. Herschel first considers the apparent effect 

 of the motion of either of the three bodies concerned, the 

 two stars, and the sun with its attendant planets ; and then 

 states the arguments respecting the motions of a few only 

 VOL. II. 



out of the fifty double stars, of which he has ascertained 

 the revolutions. The first example is Castor, or alpha 

 Geminorum : here Dr. Herschel stops to show how accu- 

 rately the apparent diameter of a star, viewed witli a con- 

 stant magnifying power, may be assumed as a measure of 

 small angular distances ; he found that ten different mir- 

 rors, of seven feet focal length, exhibited no perceptible dif- 

 ference in this respect. In the case of Castor no change of 

 the distance of the stars has been observed, but their angular 

 situation appears to have varied somewhat more than 4:)° 

 since it was observed by Dr. Bradley, in 175Q ; and they 

 have been found by Dr. Herschel in intermediate positions 

 at intermediate times. Dr. Herschel allows that it is barely 

 possible that a separate proper motion, in each of the stars 

 and in the sun, may have caused such a change in the re- 

 lative situation, but that the probability is very decidedly 

 in favour of the existence of a revolution. Its period must 

 be a little more than 342 years, and its plane nearly per- 

 pendicular to the direction of the sun. The revolution of 

 gamma leonis is supposed to be in a plane considerably 

 inclined to the line in which we view it, and to be per- 

 formed in about 1200 years. Both these revolutions are re- 

 trograde ; thatofcpsilon Bootis is direct, and is supposed to 

 occupy 1081 years, the orbit being in an oblique position with 

 respect to the sun. In zeta Herculis Dr. Herschel ob- 

 served, in 1802, the appearance of an occultation of the 

 small st.-ir by the larger one : in 1782 he had seen them 

 separate ; the plane of the revolution must therefore pass 

 nearly through the sun ; and this is all that can at present 

 be determined respecting it. The stars of delta serpentis 

 appear to perform a retrograde revolution in about 375 

 years : their ajiparent distance is invariable, as well as that 

 of the two stars which constitute gamma virginis, the last 

 double star which Dr. Herschel mentions in this paper, and 

 to which he attributes a periodical revolution of about 708 

 years. Y. 



Distance and magnitude of the 

 Stars. 



See Practical Astronomy. 



Gregory on the annual parallax of the stars. 

 Birch, in. 225. 



Suggests the observation of the distance of two neigh- 

 bouring stars. 



Roberts ou the distance of the fixed stars, 



after Hugens. Ph. tr. l694.XVni. 101. 

 Flamstead. Ph. tr. 1701. XXII. 815. 



I' u 



