24 INDEX CATALOGUE. 



Herschel, W. : Abstracts of Memoirs — Continued. 



a.d. Vol. P. 



1791 81 88 sary to inquire — we need not know the origin of the lu- 

 minous matter whose existence is rendered evident by 

 means of nebulous stars. 



1795 85 46 On the Nature and Construction. of the Sun and Fixed Stars. 



69 Speculations on the Satellites of Fixed Stars; the mutual 



distance of the component stars of condensed clusters, 

 and on the distances of the clusters themselves, etc. 



70 Star gauges. 19 h .6 to 20 h .2 ; N. P. D. = 73°.9. 



1796 86 166 Method of observing the Changes that happen to the Fixed 



stars, etc. 



1800 90 49 On the poiver of penetrating into Space by telescopes, etc. 



63 Kelative distance from the earth of cluster in Perseus and 



other clusters. 

 70-78 Observations in detail of several nebulae, each with vari- 

 ous telescopes. 



1802 92 477 Catalogue of 500 new Nebulas, Nebulous Stars, Planetary 

 Nebulae and Clusters of Stars ; with remarks on the Con- 

 struction of the Heavens. 

 After a sufficient number of celestial objects is found, there 

 is a necessity for a scientific classification. The former 

 classification was only for the convenience of the observer. 



478 Enumeration of the parts that enter into the construction 



of the heavens. 



I. Of insulated stars. 



479 Notion of an insulated star — our sun is one. 



480 The milky way consists of stars very differently scattered 



from those which are immediately about us. 



II. Of Binary Siderial Systems or Double Stars. 

 480-485 Theoretical notions of such systems. 



486 Many of them have already changed their situation with 



regard to each other in a progressive course, denoting a 

 periodical revolution round each other. 

 Our sun does not belong to such a system. 



III. Of more complicated Siderial Systems, or treble, quad- 

 ruple, quintuple, and multiple stars. 



487 Theorem as to the permanent connection of revolving stars, 



when the forces acting on any one of them reduced to a 

 direction as coming from the empty centre, are in the 

 direct ratio of the distances from that centre. 



