188 SCENERY OF THE HEAVENS. 



This planetary nebula cannot be less than 68,000,000,000, or sixty-eight thousand 

 millions, of times the size of the sun, for a globular body filling the orbit of Uranus would 

 be of that dimensions. It was first seen at Slough, in September, 1782, and is one of 

 Struve's nine rare celestial objects appended to the Dorpat catalogue of 1827. It shines 

 with a pale blue light, very bright, and has been styled a miniature of Venus. Its 

 location in space is near v Aquarii, about 10 north by west of Deneb Algedi, and 12 

 east of the great quintuple star a Capricorni. Other examples of the same class are to 

 be found near ft Ursse Majoris, y Eridani, and above the poop of Argo Navis 14 east of 

 Sirius. 



Such are the chief aspects under which nebulae, properly so called, present themselves 

 to our attention aspects diversified and singular. We observe an extremely diffused 

 filmy milk-white material, extending over immense regions, without any systematic form 

 or arrangement, as in the instance of the nebula of Orion, which may be called the rudest 

 state of the nebulous matter. We have other stars in which the material seems to wind, 

 and exhibits a congregating of the substance in distinct places, as if condensing under 

 control of a law of attraction. In other cases there is a marked structure apparent, vary- 

 ing considerably in form, but approximating to a spherical figure, with great central 

 light and condensation in other words, the appearance is that of stars surrounded with 

 a haze. However opinions may differ as to the conclusion to which these phenomena 

 point, the fact must be admitted, that a material exists and occupies extensive spaces, self- 

 luminous and phosphorescent, which presents an endless variety of contour, resembling 

 in many instances a sheet of fog, but exhibiting in others an evident aggregation into 

 distinct spherical or oblong masses. 



The natural question, " What are the nebulae ? " proposes a problem which we cannot 

 solve. It is the legitimate province, however, of the physical enquirer to study their 

 appearances, and to seize hold, if possible, of a consistent and rational interpretation. It 

 cannot be imagined that a material which occupies such tracts of space, and develops 

 itself in such peculiar forms, exists without design. " If," says Sir John Herschel, it be 

 true, as, to say the least, it seems extremely probable, that a phosphorescent or self- 

 luminous matter exists, disseminated through extensive regions in the manner of a cloud 

 or fog now assuming capricious shapes, like actual clouds drifted by the wind, and now 

 concentrating itself like a cometic atmosphere around particular stars what, we naturally 

 ask, are the nature and destination of this nebulous matter ? Is it absorbed by the stars in 

 whose neighbourhood it is found, to furnish, by its condensation, their supply of light and 

 heat ? or is it progressively concentrating itself by the effect of its own gravity into 

 masses, and so laying the foundation of new sidereal systems, or of insulated stars ? It 

 is easier to propound such questions than to offer any probable reply to them. Mean- 

 while, appeal to fact, by the method of constant and diligent observation, is open to us ; 

 and, as the double stars have yielded to this style of questioning, and disclosed a series of 

 relations of the most intelligible and interesting description, we may reasonably hope 

 that the assiduous study of the nebulae will, ere long, lead to some clearer understanding 

 of their intimate nature." From the various aspects under which the nebulous substance 

 appears diffused, without structure winding, displaying a tendency to structure 

 and in globular masses, plainly developing it it seems very probable, that these are 

 different stages of one progressive course from an inferior to a higher condition, the 

 several objects being variously advanced, yet all proceeding in the same route towards an 

 ultimate organisation. " We look among these objects," says Mr. Airy, alluding to the 

 various aspects of nebulas, and employing a happy illustration of Laplace, " as among the 

 trees of a forest. Their change in the duration of a glance is indiscoverable ; yet we 

 perceive that there are plants in all different stages. We see that these stages are 



