30 



PICTURE OF NATURE. 



other terms, of difference betwixt the relations 

 of volume and mass. When we compare the 

 planets from Mercury to Mars with the Sun 

 and with Jupiter, and Mars and Jupiter, again, 

 with Saturn, we proceed in a descending scale 

 of density ; selecting familiar objects as stand- 

 ards of comparison, from matter of the density 

 of antimony, to matter of the density of honey, 

 of water, and of pine timber. In Comets, 

 which, numerically speaking, constitute the 

 largest portion of the individualized physical 

 forms of our solar system, the most concen- 

 trated part, which we call nucleus or head, 

 still allows the light of the stars to pass through 

 it unrefracted. The mass of comets, perhaps, 

 never exceeds the five-thousandth part of the 

 mass of the earth : so variously do the forma- 

 tive processes meet us in original and perhaps 

 progressive conglobations of matter. Setting 

 out from what is most general, it was especial- 

 ly necessary to indicate this diversity, not as a 

 thing possible, but as a reality — as a datum in 

 universal space. 



What Wright, Kant, and Lambert have de- 

 duced from the conclusions of pure reason, in 

 •regard to the construction of the universe, to 

 the distribution of matter in space, has been 

 established by Sir William Herschel upon the 

 eecurer basis of observation and measurement. 

 This great, inspired, and yet cautious observer, 

 first cast the plumb-hne into the depths of 

 heaven, to determine the boundaries and the 

 form of the separate cluster of stars which we 

 inhabit ; and he was the first who ventured to 

 offer an explanation of the relations in point 

 of position and distance, of remote nebulous 

 epecks to our own astral system. William 

 Herschel, as the elegant inscription on his 

 monument, at Upton, says so happily, "broke 

 through the barriers of the heavens {cczlorum 

 perrupit daustra).^^ Like Columbus, he forced 

 his way into an unknown ocean, and caught a 

 glimpse of coasts and groups of islands whose 

 true position it is reserved for future centuries 

 to determine. 



Considerations on the varying intensity of 

 the light of the stars, and on their relative num- 

 bers — in other words, their numerical abun- 

 dance or rarity in equal fields of the telescope 

 — have led to inferences concerning the une- 

 qual distances and distribution in space of the 

 strata which they compose. Such inferences, 

 considered as leading to cfrcumscription of the 

 several portions of the universe, do not, how- 

 ever, admit of the same degree of mathemati- 

 cal certainty as is attained in all that concerns 

 our own solar system, the revolutions of double 

 stars, with unequal velocities, around a com- 

 mon centre of gravity, and the apparent or ac- 

 tual motions of the stars in general. We are 

 almost disposed to compare the chapter in our 

 physical cosmography which discusses the neb- 

 ulous specks of heaven, with the mythological 

 portion of general history. They both begin 

 alike — the one in the twihght of remote anti- 

 quity, the other in the depths of illimitable 

 space ; and where reality threatens to disap- 

 pear, fancy is doubly excited to draw from her 

 own abundance, and to give form and endurance 

 to the Indefinite and the Changeable. 



If we compare the universe with one of the 

 isle-studded oceans of our planet, we think 



that we can perceive matter distributed group, 

 wise : now, collected into unresolvable nebu- 

 lous specks of various age ; now condensed 

 around one, or several, nuclei, and again round- 

 ed into clusters of stars, or isolated sporades 

 The cluster of stars, the islet in the infinity of 

 space, to which we belong, forms a lenticular, 

 compressed, and everywhere distinct or separ- 

 ate layer, the longer axis of which has been 

 estimated at from seven to eight hundred, and 

 the shorter axis at some one hundred and fifty, 

 distances of Sirius. Presuming that the paral- 

 lax of Sirius is not greater than that of the 

 bright star in the Centaur, which has been ac- 

 curately ascertained (viz. 0" 9128), light would 

 pass through one distance of Sirius from the 

 Earth in three years, whilst, from Bessel's ad- 

 mirable earlier paper(*) on the parallax (0"-3483) 

 of the remarkable star in Cygnus (the 61st), the 

 very distinct proper motion of which must ad- 

 mit of a very close approximation, it follows, 

 that the light of this star only reaches us after 

 travelling through space for some nine years 

 and a quarter. Our stratum of stars, a disc 

 of relatively moderate thickness, is divided, 

 through one-third of its extent, into two arms ; 

 and it is thought that we are placed somewhat 

 near to this division — nearer to Sirius than to 

 the constellation of the Eagle, almost in the 

 middle of the material extension of the layer, 

 in the line of its thickness, or lesser axis. 



This position of our solar system, and the 

 formation of the whole lens, are deduced by 

 means of a process of what has been aptly des- 

 ignated gauging the heavens ; i. e. reckoning 

 the number of stars included in the same field 

 of the telescope turned on every side around. 

 The increasing, or decreasing, number of stars 

 measure the depth or thickness of the layer in 

 different directions. Precisely as the point at 

 which the plummet strikes the bottom deter- 

 mines the length of the line that it is cast from 

 the hand, do these soundings of the heavens 

 give the lengths of the visual ray, when the bot- 

 tom of the starry depths, or rather, and more 

 correctly, as there is neither above nor below 

 here, when the limits of starry space are at- 

 tained. In the direction of the longer axis, and 

 where the greatest numbers of stars lie one 

 behind another, the eye perceives the farthest 

 off thickly crowded together, connected, as it 

 seems, by a milky glimmer (light-mist), and pro- 

 jected, in perspective, upon the visible vault 

 of heaven in the form of a belt or girdle. This 

 narrow belt of beautiful, but unequal radiance, 

 for its continuity is broken by less luminous 

 spaces, divides into two branches, and, save 

 where it is interrupted for a few degrees, forms 

 a great circle upon the hollow sphere of the 

 heavens. This is in consequence of the po- 

 sition of our system, near the middle of the 

 great astral group to which it belongs, and al- 

 most in the plane of the milky way itself. 

 Were our planetary system placed far without 

 the cluster, the milky way would present itself 

 to the assisted eye as a complete ring, and. at 

 a still greater distance, as a resolvable disc- 

 shaped nebula. 



Amongst the many self-luminous bodies, er- 

 roneously designated fixed stars, for they are 

 all in motion, which constitute our island in the 

 universe, our sun is the only one which we 



