ERA OF NEWTON, HALLEY, AND HERSCHEL. 47 



four planets^ Ceres, Pallas, Juno, and Vesta, revolving round the sun at a mean distance 

 of one hundred millions of miles from Mars, so small as only to be telescopic objects. 

 This discovery we owe to Piazzi, Olbers, and Harding. Some singular features^ without 

 parallel in the planetary system, such as their close contiguity, the intersection of their 

 orbits, with their diminutive size, Vesta not being much larger than the Spanish 

 peninsula, led to the surmise that these bodies are fragments of a planet which once 

 revolved in their mean path with a magnitude proportionate to that of its neighbours. 

 The possibility of such a disruption cannot be denied the revolution of the fragments 

 round the sun would follow in obedience to the mechanical laws by which the system is 

 governed ; but the point is obviously one of those questions which must remain entirely 

 hypothetical. Next to this addition to the system, the most remarkable astronomical 

 occurrences of the present age, previous to the year 1838, are the November meteors, 

 the renewed return of Halley's comet, and the determination of the annual parallax of 

 the star 61 Cygni by Bessel. These will come under consideration in future pages, with 

 the important contributions made to science by the great names of the day, Sir John 

 Herschel, Sir James South, Struve, Airy, and Arago. - "* 



The progress of Astronomical discovery which has now been hastily traced, reminds us 

 of the obligations we owe to those who have gone before us. While supplied with facts 

 respecting the constitution of the solar universe the number, forms, magnitudes, 

 distances r and movements of its members upon the general accuracy of which the mind 

 may repose with full satisfaction ; the mode of its formation was also grappled with, and a 

 theory presented, derived from the study of the sidereal heavens, which, though now de- 

 prived of its basis, was invested with a high degree of probability. The firmament exhibits 

 dimly -luminous appearances, like patches of white cloud, displaying various forms and 

 peculiarities of structure, which are not resolvable into clusters of stars when seen through 

 common instruments, and whose phases seem at variance with the idea of stellar groups 

 indistinct and blended from their remoteness. This nebulous substance, as it has been 

 called in one of its states, resembles a sheet of fog. Under another aspect, it is seen 

 winding, and there seems a tendency towards structure, the material congregating in dif- 

 ferent places, as if under the influence of a law of attraction. Definite structure appears 

 in other cases generally assuming the spherical form, with great condensation at the 

 centre, like regular stars in the midst of a thick haze. The question was raised, What do 

 such appearances indicate ? What do the differences in their character portend ? Are the 

 nebulse tracts of self-luminous matter? Are they void and unmeaning substances in 

 a universe of organisation and order, or are they advancing by a principle of progressive 

 formation to share themselves in that order and organisation ? The idea was started, 

 that in these phenomena we have an exhibition of the first state of the now organised 

 bodies of our system, and of their progress to the ultimate conditions of their being, 

 passing from one stage of construction to another under control of the law of gravitation. 

 This is substantially the nebular hypothesis of Laplace and Herschel. It supposed a 

 diffused nebulosity, rotating with the solar nucleus, and, extending beyond the bounds of 

 the farthest planet, to have gradually condensed at the surface of the nucleus, accelerating 

 thereby the solar rotation, and increasing the centrifugal force, by the action of which 

 successive zones were detached, assuming spheroidal masses by the mutual attraction of 

 their particles. The theory enlisted a variety of evidence in its behalf, The fact of the 

 projectile motions of all the planets and satellites taking place from west to east in nearly 

 the same plane of their axical rotation- likewise being all in the same direction, and 

 corresponding with that of the solar body was viewed as an instance of extraordinary 

 coincidence strongly supporting the theory of their common origin in obedience to a 

 common law. The reflection naturally arose, that in the physical and mental constitution 



