206 



REMARKS ON TIIH PLANETOIDS BETWEEN MARS AND JUPITER. 



[1855. 



Remarks on the Planetoids between Mars and Jupiter. 



Read before the Canadian Institute, by T. Henning, Esq., March 10, 1855. 



Astronomy is, and ever must be, a study of deepest interest, 

 — wide in its range, fascinating in its details, startling in its con- 

 clusions. Of all the sciences, perhaps, it has of late years made 

 the most rapid progress. The discovery of new satellites, the 

 facts respecting single stars and binary systems, the revelations 

 of the telescope in regard to the nebulne, and, lastly, the vast 

 number of cosmical bodies which are found to be revolving in 

 space in obedience to the laws that guide and control the system 

 to which the earth belongs — all indicate the rapid strides which 

 the astronomer is making, and furnish fresh matter for wonder 

 and gratification. It is to the last of these — the numerous 

 plauet-like bodies which have of late been detected as they per- 

 formed their annual course^that I would for a few minutes 

 ■ direct your thoughts this evening, not with the view of pro- 

 pounding any new theories, but chiefly for the purpose of filling a 

 gap which has inadvertently occurred in the Papers reckoned 

 on by the Council. 



HISTORY OF THE PLANETOIDS. 



Humboldt tells us that it was an opinion of Hellenic anti- 

 quity that there were far more than five planets — that many 

 might remain unseen on account of the feebleness of their 

 light and their position. However this may be, it is certain 

 that as early as the days of Kepler, it was surmised that some 

 unseen planets occupied the space that separated Mars from 

 Jupiter. " I have become daring," says he, in a work written 

 at the youthful age of 25, " and place a new planet between 

 Jupiter and Mars, as also (a conjecture less fortunate in its re- 

 sult) another planet between Venus and jMercury ; neither of 

 these have been seen, probably on account of their extreme 

 smallness." 



Towards the close of the last century, when the distances 

 of the planets from each other and the laws which regu- 

 lated these distances came to be more intelligently discussed, 

 it was discovered that the surmises of Kepler were correct, and 

 the arithmetical progression at which he hinted was fully ex- 

 amined and dignified with the appellation of a law. This nu- 

 merical relation, which usually receives the name of Bode's 

 laio of distances, both Lalande and Delambre call " a play of 

 numbers," and others merely " a help for the memory." It 

 holds, however, so prominent a place in connection with the 

 asteroids, that a few observations^,regarding it may be neces- 

 sary. 



Commencing with Mercury, the planet nearest the Sun — the 

 grand centre of our system — and passing on from planet to 

 planet, there is a ratio of distance between each, which holds 

 true till we reach the orbit of Mars. A mighty gulpli of no 

 less than 350,000,000 of miles is then reached, in which no 

 planet was supposed to revolve, and in which the duple progres- 

 sion failed. As soon, however, as the limits of this intervening- 

 space were passed, this curious law again prevailed. Although 

 the succession of distances " does not correspond precisely with a 

 numerical series in duple progression, there is so striking an 

 approximation to it as to produce a strong impression that it must 

 be founded upon some physical cause, and not merely acciden- 

 tal." So thinks Dr. Lardner and many other distinguished 

 astronomers. Bode, however, whose name is so connected 

 with this supposed law, was not even its modern diseoverer/for 



he has stated in one of his works, that " he had taken the law 

 of the distances from a translation of Bonnet's ' Contemplation 

 de la Nature,' prepared by Professor Titius at Wittenberg." In 

 a note added to a certain chapter of the work referred to (which 

 appeared in 1772), and which I cjuote as found in the fourth 

 volume of the "Cosmos," for the purpose of showing what was 

 the scheme proposed to represent the distances of the planets, 

 Professor Titius says — -"When the distances of the planets are 

 examined, it is found that they are almost all removed from 

 each other by distances which are in the same proportion as 

 their magnitudes increase. If the distance from Saturn to the 

 Sun is taken as 100 parts, the distance of Mercury from the Sun 

 is 4 such parts (how the Professor obtained the number 4 for 

 the orbit of Mercury is not stated) ; that of Venus 4-j-3=7 

 such parts; the Earth 4+6=10; Mars 4-j-12=16. But 

 from Mars to Jupiter there is a deviation from this accurate (!) 

 progression. Mars is followed by a space of 4-|-24=28 such 

 parts, in which neither a principal planet nor a subordinate 

 planet has yet been seen. Is it possible that the Creator should 

 have left this space empty ? It cannot be doubted that this 

 space belongs to yet undiscovered satellites of Mars ; or that, 

 perhaps, even Jupiter has further satellites around him, which 

 have not hitherto been seen by any telescope. In this space, 

 (unknown to us as regards its contents) Jupiter's circle of action 

 extends to 4+48=52. Then follows Saturn in 4+96=100 

 parts — an admirable proportion." The following table will show 

 more clearly this " admirable proportion." It will be seen 

 from the last line, which represents the observed planetary dis- 

 tances, that, although not exact, there is a very close approxi- 

 mation : — 



Dis. by Bode's law.. 

 Obs. Plan. Dis 



M. 



4 

 



4 



3-9 



V. 



4 

 3 



7 



7-3 



E. 



4 

 6 



10 



10 



4 

 12 



16 



15-2 



Ast. 



4 

 24 



"2F 



27-4 



Jup. 

 4 



48 

 52 

 52 



Sat. 



4 

 96 



100 



95-4 



Ur. 



4 

 192 



196 



192 



Nep. 

 4 



384 



sss" 



Since, however, the credit of this theory is attributable to 

 Titius, if not to his predecessor Kepler, the honor of making it 

 practically useful in detecting the existence of a planet in the 

 space referred to is shared by the celebrated Baron de Zach of 

 Gotha and Professor Bode of Berlin, the former of whom is 

 said to have commenced a computation of its orbit as early as 

 1784. Under the Baron's auspices, a congress of astronomers 

 met a Lilienthal in 1800, for the purpose of agreeing to some 

 plan of hunting down this unknown body whose presence was 

 deemed almost certain. Twenty-four observers were present. 

 They agreed to divide the heavens into as many zones, giving 

 one to each astronomer. They commenced their labours on 

 the first day of the first year of the present century, and scarcely 

 had they got their instruments adjusted, before Piazzi of Paler- 

 mo, one of their number, noticed a small star of about the 7th 

 or 8th magnitude, which was not registered in his catalogue. 

 The next night, to his inexpressible delight, he found that it 

 had changed its position; that, in fact, it was a planet. 

 Baron de Zach heard of the discoveiy with great joy, com- 

 menced a computation of its orbit, the result of which satisfied 

 him, of course, of the correctness of his favourite law of rela- 

 tive distance. To this youthful member of the system Piazzi 

 gave the name of Ceres. To it has since been added the 

 large number of 32, making in all, up to the present time, a 

 group composed of 33 members, all of which, with the date of 



