596 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herschel, W.: Synopsis of the Writings of— Continued.. 

 A. D Vol. P. 



1811 101 278-281 Nebulous diffusions contain both milky nebulosity, and such as 

 from its faint appearance may be mistaken for resolvable. 

 278-279 The range of its visibility is confined to very moderate limits. 

 280 The purpose for which such great abundance of nebulosity may ex- 

 ist deserves investigation. 

 282 Either greater depth or greater compression of the nebulous matter 

 may occasion greater brightness. 



284 Condensation will best account for greater brightness. 



The condensation of the nebulous matter ascribed to gravitation. 



285 When a nebula has more than one preponderating seat of attracting 



matter, it will probably in time be divided. 

 This conception is supported by the appearance of double nebulae. 



286 Their double appearance can be no deception. 

 Their nebulosity is derived from one common stock. 



290 This opinion is supported by the remarkable situation of nebula). 

 292 Which may be seen in Mr. Bode's Ailas Ccelestis. 

 293-296 The real form of the nebulous matter of which nebulie are com- 

 posed may be inferred from their figure. 

 299 The form of the nebulous matter of round nebulse is globular. 



This form is caused by gravitation. 

 302 The central brightness of nebula? points out the seat of attraction. 

 The effect of attraction on the form of the nebulous matter depends 

 on its original expansion, on the time of the action, and on the 

 quantity of the attracting matter. 



305 III different stages of condensation pointed out. 



306 Comets may be highly condensed nebulse. 



307 Progressive condensation takes place. 



308 Concentric brightness as well as globular form indicates the general 



gravitation of the nebulous matter. 



Progressive condensation may bo seen in the formation of nuclei. 



309-310 Nebulous matter is probably capable of being consolidated; the 



act of shining x^roves it to have chemical properties. 



It will stop light, and is partly opaque. 



311 Queries relating to the subsidence of the nebulous matter, the zodiacal 



light, and the cause of rotatory motion. 

 313 Some part of the nebulous matter is probably elastic. 



313 The uniform light of nuclei, and of much condensed nebulce, proves 



that the nebulous matter is considerably opaque. 



314 When the nebulous matter assumes hardness, the progress of conden- 



sation will be impeded. 



315 Three indications of the compression of the nebulous matter. 

 Planetary api^earance arises from superficial lustre. 



316 High degree of condensation of the nebulous matter. 

 A still higher degree of condensation. 



318 In common good telescopes planetary nebulaj cannot be distinguished 



from stars. 

 Perhaps they may in the end be so condensed as actually to become 

 stars. 



319 The nebulous matter in a cubical space of 10' will admit of a con- 



densation of two trillion and 203 thousand billion times before it 

 can go into the compass of a globe of the diameter of our sun. 

 Planetary nebulce have a rotatory motion on their axes. 



