GENETIC EVOLUTION— NEBULiE. 



99 



diffused in the shape of self-luminous clouds or 

 vapours. If we first turn our attention to 

 these NEBULA (world-mists, separating into 

 determinate forms), we discover that they are 

 in course of suffering change in their state of 

 aggregation. They present themselves to our 

 eyes apparently of small dimensions, as round- 

 ed or elliptical discs, single or in pairs, occa- 

 sionally connected by a luminous streak ; of 

 larger size they are variously shaped— elonga- 

 ted or shooting out into several branches ; or 

 they look fan-shaped ; or they form sharply de- 

 fined rings with dark included centres. These 

 nebulae are believed to be in process of various 

 and progressive changes, according as the star- 

 dust or vapour composing them is becoming 

 condensed, in harmony with the laws of at- 

 traction, around one or several nuclei. The 

 number of these unresolvable nebulae — nebulae 

 in which the most powerful telescope does not 

 enable us to distinguish a single star — that 

 have been reckoned, and their position in space 

 determined, now amounts to about one thou- 

 sand five hundred. 



The genetic evolution, the ceaseless, pro- 

 gressive formation that appears to be going on 

 in these portions of infinite space, has led re- 

 flective minds to the analogy of organic phe- 

 nomena. As in our woods we observe the 

 same kind of tree in every stage of growth at 

 the same time, and from this view, this co-ex- 

 istence, derive the impression of progressive 

 vital development ; so do we, in the mighty 

 garden of the universe, recognise different sta- 

 ges in the progressive formation of stars. The 

 process of condensation, indeed, which Anax- 

 imenes and the Ionic school once taught, seems 

 here to proceed, as it were, under our eyes. 

 This object of inquiry and conjecture is pecu- 

 liarly attractive to the imagination. That 

 which, in the circles of life, and in all the in- 

 ternal impulsive forces of the universe, fetters 

 us so unspeakably, is less the recognition of 

 Being, than of what is About to be ; even 

 though the latter be nothing more than a new 

 condition of matter already extant ; for of 

 proper creation as an efficient act, of a proto- 

 genesis of matter, of entity succeeding nonen- 

 tity, we have neither conception nor expe- 

 rience. 



It is not merely by a comparison of the various 

 moments of development which are exhibited 

 by nebulae, in greater or less degrees of con- 

 densation of their interiors, that astronomers 

 have inferred changes in their structure. We 

 have now a series of observations made imme- 

 diately upon particular nebulae, on the one in 

 Andromeda, on that which occurs in the ship 

 Argo, and also in the flocky portion of that 

 which presents itself in Orion, which led to the 

 belief that actuzJ changes in their form have 

 been observed. Inequahty of power of light in 

 the instruments employed, however, different 

 states of our atmosphere, and other optical 

 conditions, it must be admitted, render a por- 

 tion of these results questionable as true his- 

 torical data. 



The peculiar multiform nebulae, the several 

 parts of which have different degrees of bright- 

 ness, and which, with a diminution of their 

 areas, will perhaps become concentrated into 

 stars, and those nebulae that have been entitled 



planetary, the round or somewhat oviform 

 discs of which shine in every part with a mild 

 and equable light, are not to be confounded 

 with nebulous stars. Here there is no appear- 

 ance of a star projected accidentally, as it 

 might seem, upon a remote nebulous ground ; 

 no, the vaporiform matter, the light-cloud, 

 forms a single mass with the star which it sur- 

 rounds. From the frequently very considera- 

 ble magnitude of their apparent diameters, and 

 the distances whence they glimmer, both plan- 

 etary nebulae and nebulous stars must possess 

 enormous dimensions. New and acute con- 

 siderationsO on the very different influence of 

 distance upon the intensity of the light of a 

 disc of measurable diameter, or of a single 

 self-luminous point, make it not improbable that 

 planetary nebulae are extremely remote nebu- 

 lous stars, in which the distinction between the 

 central star and its hazy envelope has disap- 

 peared even to our telescopic vision. 



The brilliant zones of the southern celestial 

 hemisphere, between the parallels of 50° and 

 80°, are particularly rich in nebulous stars, and 

 concentrated but unresolvable nebulae. The 

 Magellanic clouds which circulate round the 

 starless, desolate south pole (especially the 

 larger of the two), appear, according to the la- 

 test observations('), " as a wonderful mixture 

 of groups of stars, of globular clusters of nebu- 

 lous stars of different magnitudes, and of un- 

 resolvable nebulaj, which, producing a general 

 brightness of the field of vision, form a kind of 

 back-ground to the picture." The aspect of 

 these clouds, of the light-streaming ship Argo, 

 of the milky way between the Scorpion, the 

 Centaur, and the Cross — the whole of the 

 charming landscape presented by the southern 

 heavens, has left an indelible impression upon 

 my mind. The zodiacal light, which rises like 

 a pyramid from the sun, and in its gentle ra- 

 diance proves another of the eternal ornaments 

 of the tropical night, is either an immense neb- 

 ulous ring rotating betwixt the earth and Mars, 

 or (but this is less probable) it is the outermost 

 stratum of the sun's atmosphere itself Be- 

 sides these luminous clouds and nebulae of de- 

 terminate form, accurate and still coinciding 

 observations seem to proclaim the existence 

 and general diffusion of an infinitely rare, and 

 apparently not self-luminous matter, which, 

 OFFERING RESISTANCE, rcveals itsclf by lessen- 

 ing the eccentricity, and shortening the period 

 of revolution of Encke's, and perhaps also of 

 Biela's comet. This impeding aethereal and 

 cosmic matter may be conceived as in motion, 

 despite its original tenuity as gravitating, as 

 condensed in the vicinity of the great body of 

 the sun, and even as increased in the course 

 of myriads of years, by vapours thrown off 

 from the tails of comets. 



If we now pass on from the nebulous matter 

 of the infinities of heavenly spiace (ovpavov x'^P' 

 Toc% here scattered without form or boundary, 

 a cosmic world-ether, there condensed into neb- 

 ulous specks, to the .conglobated solid portions 

 of the universe, we approach a class of phenom- 

 ena which are exclusively designated by the title 

 of stars, or fixed stars. And here, too, the de- 

 gree of solidity or density of the conglobated 

 matter is different. Our own solar system pre- 

 sents us with every grade of mean density ;. in 



