24 NEBULOUS STATE OF MATTER. 



views with eagerness, as confirming theoretical conclu- 

 sions deduced from an examination of the structure of 

 the earth itself, and explained by them the gradual 

 accretion of atoms into crystalline rocks from a cooling 

 mass. 



of rotatoiy motion ; and an exterior zone of vapour was detached 

 from the rest, the central attraction being no longer able to over- 

 come the increased centrifugal force. This zone of vapour might 

 in some cases retain its form, as we see it in Saturn's ring ; but 

 more usually the ring of vapour would break into several masses, 

 and these would generally coalesce into one mass, which would re- 

 volve about the sun." WhewelTs Eridgewater Treatise. 



The following passage is translated by the same author from 

 Laplace : 



' " The anterior state (a state of cloudy brightness) was itself pre- 

 ceded by other states, in which the nebulous matter was more and 

 more diffuse, the nucleus being less and less luminous. We arrive 

 in this manner at a nebulosity so diffuse, that its existence could 

 scarce be suspected. Such is in fact the first state of the nebula 

 which Herschel carefully observed by means of his telescope." 



Sir William Herschel has the following observations on these 

 remarkable masses : 



" The nature of planetary nebulae, which has hitherto been in- 

 volved in much darkness, may now be explained with some degree 

 of satisfaction, since the uniform and very considerable brightness 

 of their apparent disc accords remarkably well with a much con- 

 densed, luminous fluid; whereas, to suppose them to consist of 

 clustering stars will not so completely account for the milkiness or 

 soft tint of their light, to produce which it would be required that 

 the condensation of the stars should be carried to an almost incon- 

 ceivable degree of accumulation. 



" How far the light that is perpetually emitted from millions of 

 suns may be concerned in this shining fluid, it might be presump- 

 tuous to attempt to determine; but notwithstanding the incon- 

 ceivable subtilty of the particles of light, when the number of the 

 emitting bodies is almost infinitely great, and the time of the con- 

 tinual emission indefinitely long, the quantity of emitted particles 

 may well become adequate to the constitution of a shining fluid or 

 luminous matter, provided a cause can be found that may retain 

 them from flying off, or reunite them. 3 ' Observations on Nebulous 

 Stars: Philosophical Transactions, vol. Ixxxi. A.D. 1791. 



In addition, the following Memoirs on the same subject, by Sir 

 William Herschel, have been published in the Philosophical Trans- 

 actions ICatalogue of 1000 Nebulae and Clusters of Stars, vol. 



