BIBLIOGRAPHY OF IIERSCIIEL's WRITINGS. 607 



Herschel W.; Synovsis of the Wiutings of— Continued. 



A. D. Tol. P. 



1815 105 345 Comidcralion of the prhiciphs hy which the periodical revolution of itie 

 satcJlitca may he obtained from the observed aiujles of poHilion. 

 348 The periodical rcrohiiious of the satellites dctirviiued. 



350 The first satellite [ Titania] makes a synodical revolution in 8'' IC^ 56"" 



5.2^ and the second lObcron] in 13'' ll^' S"" 5'J». 



351 Explanation of the identifying method. 



355 I. With the lij;ht of my 20-foot telescope the first satellite generally 



becomes invisible at a distance of [18"] from the planet; and 



II. The second at about [24"]. 



III. An interior satellite cannot be seen two nights in succession. 



356 IV. Exterior satellites that are very faint when at their greatest 



elongation can hardly ever he seen at any other time when the 

 orbits are contracted. 



V. iTitania'} is probably larger than lObcron]. 



VI. Both are subject to great variations of light [not owing to the 

 changeable clearness of the air]. 



VII. This may be due to a rotation on their axes, or from atmos- 

 pheres. 



VIII. I have supposed the distances of the first and second satellites 

 to be 36" and 48" respectively. 



IX. The existence of additional satellites has been considered akeady 

 in Phil. Trans., 1798, p. 59. 



358 An interior satellite. 



359 Addition [in regard to an interior satellite]. 



360 An intermediate saiellite. An extei-ior satellite; and Addition. 



361 More distant satellites ; and Addition. 



362 Plate XVI, diagram. 



1817 107 302 Astronomical Obserrations and Experiments tending to inrestigaie the local 

 Arrangement of the Celestial Bodies in Space and to determine the Exten 

 and Condition of the MUky Way. By Sir William Hersc.iel, Knt. 

 Gnelv., LL. D., F. R. S. Read June 19, 1817. 



302 The construction of the heavens can only bo known when we have 



the situation of each body defined by its three dnnensums. Of 

 these three the ordinary catalogues give but two, leaving the dis- 

 tance or profundity undetenniued. 



303 The method of parallaxes has given the distance of the sun, planets 



etc. The parallax of the stars has also received attention ^^ . h 

 rc^ard to more distant objects, as small stars, compressed clusters, 

 an"d nebuhe, these methods can give us no assistance. 



303 I. Of the local situation of the stars of the Heavens. 



304 It is evident that we cannot mean to affirm that the stars of the fifth 



sixth, and seventh magnitudes are really smaller than those of he 

 first second or third, and that we must ascribe the cause of the 

 ^:Zr;n the appaU magnitudes of the stars^to a^^^-^ - 

 their relative distances from us. On account of the S^f^^'^^^J 

 of stars in each class we must also allow that the «tarsof ea h sue 

 ceedin.r ma-uitude beginning with the first, arc, one ^^ ith ano her, 



;h:r^::^ us than tlS.se of the magnitude iinmediateyp^ 

 Therelativemagnitudesgiveonlyrelativedistances . dcana^^^^^^^ 



no information as to the real distances at which ^^''^ f^^ ^smay be 

 304 II. Of a standard by which the relative arrangement of the stars maj 



aX:^ of reference ^r the arrangement of the stars may he had 



