208 



REMARKS ON THE PLANETOIDS BETWEEN MARS AND JUPITER. 



[1855. 



an investigation to ascertain the amount of force neces- 

 sary to burst a planet and separate its fragments. " The 

 possibility of determining by calculation, even approxi- 

 mately, the epoch of such a cosmical event as the destruction 

 of a planet," Humboldt considers " more than doubtful, from 

 the complication produced by the already large number of the 

 ' fragments' known, the peculiar retrogression of the apsides 

 and motion of the nodes." This has not, however, deterred 

 ino'cnious men from investigations respecting this " destroyed 

 planet." Mr. Daniel Kirkwood, of Delaware College, United 

 States has even ventured to restore from the fragments which 

 remain the primitive planet, in the same manner as others 

 have attempted to restore the animals of the primitive earth. 

 He finds for it a diameter greater than Mars (of more than 4320 

 o-eographical miles), and gives it the slowest rotation of all the 

 priiKiipal planets and a length of day of 57 hours and a half An- 

 other American, Professor Alexander, concludes, from the mean 

 of two results separately obtained, that the equatorial diameter 

 of the supposed parent planet was about 50,000 miles, while its 

 polar diameter was scarcely greater than the thickness of the 

 bright rings of Saturn. 



As illustrative of the mode in which this supposed original 

 planet may have been broken up, Mr. Nasmyth, in a paper read 

 before the British Association in 1853, referred to the case of 

 the well known toy called " Prince Rupert's drop," viz.: " A 

 drop of glass which has been let fall while in a semi-fluid state 

 into water, by which the surface of the glass drop is caused to 

 cool and consolidate so rapidly that the subsequent conso- 

 hdation and contraction of the interior mass induces such a high 

 degree of tension between it and the exterior crust, that the 

 slightest vibration is sufiieient to overcome the cohesion of the 

 external crust, and by so letting free the state of tension to cause 

 the glass drop to fly into thousands of fragments." Applying 

 this to the case of the parent planet of the asteroids, he says : 

 " It may have consisted of such materials as that by the rapid 

 passing of its surface from the original molten condition to that 

 of solidification, while the yet fluid or semi-fluid went on con- 

 tracting by the comparatively gradual escape of its heat into 

 space through the solid crust, a state of tension may thereby 

 have been induced, such as that in the ' Rupert's drop,' and 

 that the crust may have at last given way with such violence as 

 to cause the fragments to part company, and to pass off, whirl- 

 ing into orbits, slightly varying fromeach other, according to 

 corresponding variations in the condition of each at the instant 

 of rupture." 



With the progress of discovery, opinions change. The great 

 inclination ot the orbit of Pallas had long'presented a difficulty to 

 those who supported the hypothesis of Olbers. The numerous 

 additions made yearly to the sum of the small planets, have 

 confirmed some astronomers in the opinion that the planetoids 

 were formed in the same manner, and according to the same 

 laws, as the other heavenly bodies — that no alteration, in fact, 

 had occurred in the primitive system of the universe. While 

 examining, during last winter, the opinions of astronomers in 

 regard to "the small cosmical bodies denominated meteors or fall- 

 ing stars, I had a strong impression that the asteroids would be 

 found to be similar to these in origin and character, as well as 

 destiny. I was afterwards confirmed in this opinion by a paper 

 written by LeYerrier, and published in SUliman' s Journal for 

 July, 1854, in which he overturns the views of Olbers regarding 

 the perturbation of the orbits of the planets, caused by their mu- 

 tual attraction ; and after a thorough investigation of the secular 

 variations of the elements of the orbits, establishes, amongst 



others, the following propositions : — " 1. The eccentricities of 

 the orbits of the known asteroids can suffer only very small 

 changes as the effect of perturbation. These eccentricities, 

 which are now quite large, have then always been and will 

 always remain large. 2. The same is true of the inclination of 

 their orbits. So that the amount of eccentricity and inclina- 

 tion answers to the primitive conditions of the formation of the 

 group." 



Amongst the latest hypotheses on the subject of the aster- 

 oids, I may state the opinion of the author of that remarkable 

 book, " The Plurality of Worlds," who, it is pretty well known, 

 is Professor Whewell.* " The near coincidence," says he, " of 

 the orbits of the small bodies between jNIars and Jupiter, has 

 suggested to astronomers the conjecture that they have resulted 

 from the explosion of a larger body, and from its fracture into 

 fragments. Perhaps the general phenomena of the universe 

 suggest, rather, the notion of a collapse of portions of sidereal 

 matter, than of a sudden disruption and dispersion of any por- 

 tion of it; and these small bodies may be the results of some 

 imperfectly effected concentration of the elements of our sys- 

 tem, which, if it had gone on more completely and regularly, 

 might have produced another planet like Mars or Venus. Per- 

 haps they are only the larger masses among a great number of 

 smaller ones, resulting from such a process; and it is very 

 conceivable that the meteoric stones are other results of the like 

 process — -hits of planets which have failed in the making, and 

 lost their way, till arrested by the resistance of the Earth's at- 

 mosphere. Their great eccentricity, great deviation from the 

 zodiacal path, and their great number all fall in with the sup- 

 position that there are in the solar system a vast multitude ol 

 such abnormal planetoidal lumps." 



In a paper on " New Theories of the Universe," prepared 

 for presentation to the British Association at the meeting last 

 year, and with a copy of which I have been favored, the author, 

 James Bedford, Ph.D., of New Brighton, advances some start- 

 ling doctrines, amongst which is the following regarding these 

 bodies :-^" The asteroids," he believes, "were projected in 

 one mass from the sun, as were all the other primary planets ; 

 but, like a snowball thrown into the air when not sufficiently 

 compacted, the mass separated where they are found ; hence 

 they all move in the same direction as the other planets, which 

 could not be accounted for, if, as some terrifyingly suppose, they 

 were originally a world that burst asunder. Verily, a planet 

 once sufficiently condensed", cooled down from its igneous state 

 to become a habitable globe, will never burst." 



The following are the most remarkable peculiarities of this 

 group of planets : — 



1. They are exceedingly small, the largest being at the ut- 

 most only 145 geographical miles in diameter. Le Verrier 

 concludes that the sum total of the matter constituting those 

 situated between the mean distances of 2° 20' and 3° 16' can- 

 not exceed about one-fourth of the mass of the Earth. 



2. They occupy a distinct zone in which they circulate, and 

 thus clearly indicate the existence of some peculiar family re- 

 lationship. 



3. The inclinations of their orbits range from zero up to 35° ; 

 and the eccentricities from near zero up to more than one 



* Since the above was written, it Las been found that Mr. J. S. 

 Smith, of Balliol College, Oxford, not Dr. Whewell, is the author of 

 ihe " PluraUty of Worlds." 



