9*2 



to. Nebulous 



ifcars. 



jz. Planetary 



nebulae. 



ON THE CONSTRUCTION OP THE HEAVENS. 



faw, as it were, through an opening into a region of light*. 

 Much more would he be convinced now, when changes in its 

 fhapeand luftre have been feen, that its light is not, like that 

 of the milky-way, compofed of ftars. To attempt even a guefs 

 at what this light may be, would be prefumptuous. If it 

 fhould be furmifed, for inftancq, that this nebulofity is of the 

 nature of the zodiacal light, we mould then be obliged to ad- 

 mit the exiftence of an effect without its caufe. An idea of 

 its phofphorical condition, is not more philofophical, unlefs we 

 could fhew from what fource of phofphorical matter, fuch im- 

 meafurable traces of luminous phenomena could draw their 

 exiftence, and permanency ; for, though minute changes have 

 been obferved, yet a general refemblance, allowing for the 

 difference of telefcopes, is ftill to be perceived in the great 

 nebulofity of Orion, even fince the time of its firft difcovery. 



X. Of Nebulous Stars. 



The nature of thefe remarkable objects is enveloped in much 

 obfcurity. It will probably require ages of obfervations, before 

 we can be enabled to form a proper eflimate of their condi- 

 tion. That ftars fhould have vifible atmofpheres, of fuch an 

 extent as thofe of wjiich I have given the fituation in this and 

 my former catalogues, is truly furprifing, unlefs we attribute 

 to fuch atmofpheres, the quality of felf-luminous milky nebulo- 

 fity. We can have no reafon to doubt of the ftarry nature of 

 the central point ; for, in no refpedt whatever does its appear- 

 ance differ from that of a ftar of an equal magnitude ; but, 

 when the great diflance of fuch ftars is taken into considera- 

 tion, the real extent of the furrounding nebulofity is truly 

 wonderful. A very curious one of this kind will be found in 

 the 4th clafs, No. 69. 



XI. Planetary Nebula. 



Thisfeems to be a fpecies of bodies that demands a particu- 

 lar attention. To inveftigate the planetary nature of thefe 

 nebulce, is not an eafy undertaking. If we admit them to con- 

 tain a great mafs of matter, fuch as that of which our fun is 

 compofed, and that they are, like the fun, furrounded by denfe 

 luminous clouds, it appears evidently that the intrinfic bright- 

 wfc of thefe clouds mull be far inferior to thofe of the fun, A 



* See Syjle?na Saturnium, page 8 and 9, 



part 



