28 INDEX CATALOGUE. 



Herschel, W. : Abstracts of Memoirs — Continued. 



Very distant nebulosities which cannot be seen in a state of 

 diffusion may become visible when condensed into sepa- 

 rate nebulae. 



Conversion of planetary into bright stellar nebula?, into 

 stars with burs, or star9 with haziness. 



Conversion of more distant ones into faint stellar nebulae, 

 into stars with burs or with faint chevelure. 



"When it is doubtful whether an object is a star or a nebula, 

 it may be verified by an increase of magnifying power. 

 330 When the object is very like a star it becomes difficult to 

 ascertain whether it is a star or a nebula. 



When we cannot ascertain whether the doubtful object is 

 a star or a nebula, of which several instances are given, 

 the similitude is as great as any we can expect ; for were 

 it greater there could be no doubt. 

 1814 104 24-3 Astronomical Observations relating to the Siderial part of 

 the Heavens and its Connection with the Nebulous part ; 

 arranged for the purpose of a critical examination. 



In the memoir on the nebulous part of the heavens [P. T. 

 1811] I have endeavored to show the probability of a 

 very gradual conversion of the nebulous matter into the 

 siderial appearance. 



249 1. Of stars in remarkable situations in regard to Nebulae. 

 Surmise that nebulae may have considerable proper motions. 



Necessity of caution in such conclusions. Five stars in 

 such situations. 



250 II. Of two stars with nebulosity between them. 



19 instances of such connection are given ; in the memoir 

 of 1811, 139 double nebulae joined by nebulosity were 

 noted. 



251 Should we not surmise that possibly these stars had form- 



erly been highly condensed nebulae like those that had 

 been mentioned, and were now by gradually increasing 

 condensation turned into small stars; and may not the 

 nebulosity still remaining show their nebulous origin ? 

 Also we have over 700* double stars free from nebulosity, 

 many of which are probably at no great real distance 

 from us, it seems as if we had these double objects in 

 three different successive conditions. 1st, as nebulae; next 

 as stars with remaining nebulosity; and lastly, as stars 

 completely free from nebulous appearance. 



I * 10.0110 or more in 1870. As comparatively few are nebulous, either our system 

 is in an advanced state or tlie order here given is exceptional.] 



