The Asteroids.
by Daniel Kirkwood.
PREFACE.
The rapid progress of discovery in the zone of minor planets, the anomalous forms and positions of their orbits, the small size as well as the great number of these telescopic bodies, and their peculiar relations to Jupiter, the ma.s.sive planet next exterior,--all ent.i.tle this part of the system to more particular consideration than it has. .h.i.therto received. The following essay is designed, therefore, to supply an obvious want. Its results are given in some detail up to the date of publication. Part I. presents in a popular form the leading historical facts as to the discovery of Ceres, Pallas, Juno, Vesta, and Astraea; a tabular statement of the dates and places of discovery for the entire group; a list of the names of discoverers, with the number of minor planets detected by each; and a table of the princ.i.p.al elements so far as computed.
In Part II. this descriptive summary is followed by questions relating to the origin of the cl.u.s.ter; the elimination of members from particular parts; the eccentricities and inclinations of the orbits; and the relation of the zone to comets of short period. The elements are those given in the Paris _Annuaire_ for 1887, or in recent numbers of the _Circular zum Berliner Astronomischen Jahrbuch_.
DANIEL KIRKWOOD.
BLOOMINGTON, INDIANA, November, 1887.
PART I.
THE ASTEROIDS, OR MINOR PLANETS BETWEEN MARS AND JUPITER.
1. Introductory.
PLANETARY DISCOVERIES BEFORE THE ASTEROIDS WERE KNOWN.
The first observer who watched the skies with any degree of care could not fail to notice that while the greater number of stars maintained the same relative places, a few from night to night were ever changing their positions. The planetary character of Mercury, Venus, Mars, Jupiter, and Saturn was thus known before the dawn of history. The names, however, of those who first distinguished them as "wanderers" are hopelessly lost.
Venus, the morning and evening star, was long regarded as two distinct bodies. The discovery that the change of aspect was due to a single planet"s change of position is ascribed to Pythagoras.
At the beginning of the seventeenth century but six primary planets and one satellite were known as members of the solar system. Very few, even of the learned, had then accepted the theory of Copernicus; in fact, before the invention of the telescope the evidence in its favor was not absolutely conclusive. On the 7th of January, 1610, Galileo first saw the satellites of Jupiter. The bearing of this discovery on the theory of the universe was sufficiently obvious. Such was the prejudice, however, against the Copernican system that some of its opponents denied even the reality of Galileo"s discovery. "Those satellites," said a Tuscan astronomer, "are invisible to the naked eye, and therefore can exercise no influence on the earth, and therefore would be useless, and therefore do not exist. Besides, the Jews and other ancient nations, as well as modern Europeans, have adopted the division of the week into _seven_ days, and have named them from the seven planets; now, if we increase the number of planets this whole system falls to the ground."
No other secondary planet was discovered till March 25, 1655, when t.i.tan, the largest satellite of Saturn, was detected by Huyghens. About two years later (December 7, 1657) the same astronomer discovered the true form of Saturn"s ring; and before the close of the century (1671-1684) four more satellites, j.a.petus, Rhea, Tethys, and Dione, were added to the Saturnian system by the elder Ca.s.sini. Our planetary system, therefore, as known at the close of the seventeenth century, consisted of six primary and ten secondary planets.
Nearly a century had elapsed from the date of Ca.s.sini"s discovery of Dione, when, on the 13th of March, 1781, Sir William Herschel enlarged the dimensions of our system by the detection of a planet--Ura.n.u.s--exterior to Saturn. A few years later (1787-1794) the same distinguished observer discovered the first and second satellites of Saturn, and also the four Uranian satellites. He was the only planet discoverer of the eighteenth century.
2. Discovery of the First Asteroids.
As long ago as the commencement of the seventeenth century the celebrated Kepler observed that the respective distances of the planets from the sun formed nearly a regular progression. The series, however, by which those distances were expressed required the interpolation of a term between Mars and Jupiter,--a fact which led the ill.u.s.trious German to predict the discovery of a planet in that interval. This conjecture attracted but little attention till after the discovery of Ura.n.u.s, whose distance was found to harmonize in a remarkable manner with Kepler"s order of progression. Such a coincidence was of course regarded with considerable interest. Towards the close of the last century Professor Bode, who had given the subject much attention, published the law of distances which bears his name, but which, as he acknowledged, is due to Professor t.i.tius. According to this formula the distances of the planets from Mercury"s...o...b..t form a geometrical series of which the ratio is two. In other words, if we reckon the distances of Venus, the earth, etc., from the orbit of Mercury, instead of from the sun, we find that--interpolating a term between Mars and Jupiter--the distance of any member of the system is very nearly half that of the next exterior.
Baron De Zach, an enthusiastic astronomer, was greatly interested in Bode"s empirical scheme, and undertook to determine the elements of the hypothetical planet. In 1800 a number of astronomers met at Lilienthal, organized an astronomical society, and a.s.signed one twenty-fourth part of the zodiac to each of twenty-four observers, in order to detect, if possible, the unseen planet. When it is remembered that at this time no primary planet had been discovered within the ancient limits of the solar system, that the object to be looked for was comparatively near us, and that the so-called law of distances was purely empirical, the prospect of success, it is evident, was extremely uncertain. How long the watch, if unsuccessful, might have been continued is doubtful. The object of research, however, was fortunately brought to light before the members of the astronomical a.s.sociation had fairly commenced their labors.[1]
On the 1st of January, 1801, Professor Giuseppe Piazzi, of Palermo, noticed a star of the eighth magnitude, not indicated in Wollaston"s catalogue. Subsequent observations soon revealed its planetary character, its mean distance corresponding very nearly with the calculations of De Zach. The discoverer called it Ceres Ferdinandea, in honor of his sovereign, the King of Naples. In this, however, he was not followed by astronomers, and the planet is now known by the name of Ceres alone. The discovery of this body was hailed by astronomers with the liveliest gratification as completing the harmony of the system.
What, then, was their surprise when in the course of a few months this remarkable order was again interrupted! On the 28th of March, 1802, Dr.
William Olbers, of Bremen, while examining the relative positions of the small stars along the path of Ceres, in order to find that planet with the greater facility, noticed a star of the seventh or eighth magnitude, forming with two others an equilateral triangle where he was certain no such configuration existed a few months before. In the course of a few hours its motion was perceptible, and on the following night it had very sensibly changed its position with respect to the neighboring stars.
Another planet was therefore detected, and Dr. Olbers immediately communicated his discovery to Professor Bode and Baron De Zach. In his letter to the former he suggested Pallas as the name of the new member of the system,--a name which was at once adopted. Its...o...b..t, which was soon computed by Gauss, was found to present several striking anomalies.
The inclination of its plane to that of the ecliptic was nearly thirty-five degrees,--an amount of deviation altogether extraordinary.
The eccentricity also was greater than in the case of any of the old planets. These peculiarities, together with the fact that the mean distances of Ceres and Pallas were nearly the same, and that their orbits approached very near each other at the intersection of their planes, suggested the hypothesis that they are fragments of a single original planet, which, at a very remote epoch, was disrupted by some mysterious convulsion. This theory will be considered when we come to discuss the tabulated elements of the minor planets now known.
For the convenience of astronomers, Professor Harding, of Lilienthal, undertook the construction of charts of all the small stars near the orbits of Ceres and Pallas. On the evening of September 1, 1804, while engaged in observations for this purpose, he noticed a star of the eighth magnitude not mentioned in the great catalogue of Lalande. This proved to be a third member of the group of asteroids. The discovery was first announced to Dr. Olbers, who observed the planet at Bremen on the evening of September 7.
Before Ceres had been generally adopted by astronomers as the name of the first asteroid, Laplace had expressed a preference for Juno. This, however, the discoverer was unwilling to accept. Mr. Harding, like Laplace, deeming it appropriate to place Juno near Jupiter, selected the name for the third minor planet, which is accordingly known by this designation.
Juno is distinguished among the first asteroids by the great eccentricity of its...o...b..t, amounting to more than 0.25. Its least and its greatest distances from the sun are therefore to each other very nearly in the ratio of three to five. The planet consequently receives nearly three times as much light and heat in perihelion as in aphelion.
It follows, also, that the half of the orbit nearest the sun is described in about eighteen months, while the remainder, or more distant half, is not pa.s.sed over in much less than three years. Schroeter noticed a variation in the light of Juno, which he supposed to be produced by an axial rotation in about twenty-seven hours.
The fact that Juno was discovered not far from the point at which the orbit of Pallas approaches very near that of Ceres, was considered a strong confirmation of the hypothesis that the asteroids were produced by the explosion of a large planet; for in case this hypothesis be founded in truth, it is evident that whatever may have been the forms of the various...o...b..ts a.s.sumed by the fragments, they must all return to the point of separation. In order, therefore, to detect other members of the group, Dr. Olbers undertook a systematic examination of the two opposite regions of the heavens through which they must pa.s.s. This search was prosecuted with great industry and perseverance till ultimately crowned with success. On the 29th of March, 1807, while sweeping over one of those regions through which the orbits of the known asteroids pa.s.sed, a star of the sixth magnitude was observed where none had been seen at previous examinations. Its planetary character, which was immediately suspected, was confirmed by observation, its motion being detected on the very evening of its discovery. This fortunate result afforded the first instance of the discovery of two primary planets by the same observer.
The astronomer Gauss having been requested to name the new planet, fixed upon Vesta, a name universally accepted. Though the brightest of the asteroids, its apparent diameter is too small to be accurately determined, and hence its real magnitude is not well ascertained.
Professor Harrington, of Ann Arbor, has estimated the diameter at five hundred and twenty miles. According to others, however, it does not exceed three hundred. If the latter be correct, the volume is about 1/20000 that of the earth. It is remarkable that notwithstanding its diminutive size it may be seen under favorable circ.u.mstances by the naked eye.
Encouraged by the discovery of Vesta (which he regarded as almost a demonstration of his favorite theory), Dr. Olbers continued his systematic search for other planetary fragments. Not meeting, however, with further success, he relinquished his observations in 1816. His failure, it may here be remarked, was doubtless owing to the fact that his examination was limited to stars of the seventh and eighth magnitudes.
The search for new planets was next resumed about 1831, by Herr Hencke, of Driessen. With a zeal and perseverance worthy of all praise, this amateur astronomer employed himself in a strict examination of the heavens represented by the Maps of the Berlin Academy. These maps extend fifteen degrees on each side of the equator, and contain all stars down to the ninth magnitude and many of the tenth. Dr. Hencke rendered some of these charts still more complete by the insertion of smaller stars; or rather, "made for himself special charts of particular districts." On the evening of December 8, 1845, he observed a star of the ninth magnitude where none had been previously seen, as he knew from the fact that it was neither found on his own chart nor given on that of the Academy. On the next morning he wrote to Professors Encke and Schumacher informing them of his supposed discovery. "It is very improbable," he remarked in his letter to the latter, "that this should prove to be merely a variable star, since in my former observations of this region, which have been continued for many years, I have never detected the slightest trace of it." The new star was soon seen at the princ.i.p.al observatories of Europe, and its planetary character satisfactorily established. The selection of a name was left by the discoverer to Professor Encke, who chose that of Astraea.
The facts in regard to the very numerous subsequent discoveries may best be presented in a tabular form.
TABLE I.
_The Asteroids in the Order of their Discovery._
-----------------+----------------+---------------+------------ Asteroids.Date ofName ofPlace ofDiscovery.Discoverer.Discovery.
-----------------+----------------+---------------+------------ 1. Ceres1801, Jan. 1PiazziPalermo 2. Pallas1802, Mar. 28OlbersBremen 3. Juno1804, Sept. 1HardingLilienthal 4. Vesta1807, Mar. 29OlbersBremen 5. Astraea1845, Dec. 8HenckeDriessen 6. Hebe1847, July 1HenckeDriessen 7. Iris1847, Aug. 14HindLondon 8. Flora1847, Oct. 18HindLondon 9. Metis1848, Apr. 26GrahamMarkree 10. Hygeia1849, Apr. 12De GasparisNaples 11. Parthenope1850, May 11De GasparisNaples 12. Victoria1850, Sept. 13HindLondon 13. Egeria1850, Nov. 2De GasparisNaples 14. Irene1851, May 19HindLondon 15. Eunomia1851, July 29De GasparisNaples 16. Psyche1852, Mar. 17De GasparisNaples 17. Thetis1852, Apr. 17LutherBilk 18. Melpomene1852, June 24HindLondon 19. Fortuna1852, Aug. 22HindLondon 20. Ma.s.salia1852, Sept. 19De GasparisNaples 21. Lutetia1852, Nov. 15GoldschmidtParis 22. Calliope1852, Nov. 16HindLondon 23. Thalia1852, Dec. 15HindLondon 24. Themis1853, Apr. 5De GasparisNaples 25. Phocea1853, Apr. 6ChacornacMa.r.s.eilles 26. Proserpine1853, May 5LutherBilk 27. Euterpe1853, Nov. 8HindLondon 28. Bellona1854, Mar. 1LutherBilk 29. Amphitrite1854, Mar. 1MarthLondon 30. Urania1854, July 22HindLondon 31. Euphrosyne1854, Sept. 1FergusonWashington 32. Pomona1854, Oct. 26GoldschmidtParis 33. Polyhymnia1854, Oct. 28ChacornacParis 34. Circe1855, Apr. 6ChacornacParis 35. Leucothea1855, Apr. 19LutherBilk 36. Atalanta1855, Oct. 5GoldschmidtParis 37. Fides1855, Oct. 5LutherBilk 38. Leda1856, Jan. 12ChacornacParis 39. Laet.i.tia1856, Feb. 8ChacornacParis 40. Harmonia1856, Mar. 31GoldschmidtParis 41. Daphne1856, May 22GoldschmidtParis 42. Isis1856, May 23PogsonOxford 43. Ariadne1857, Apr. 15PogsonOxford 44. Nysa1857, May 27GoldschmidtParis 45. Eugenia1857, June 27GoldschmidtParis 46. Hestia1857, Aug. 16PogsonOxford 47. Aglaia1857, Sept. 15LutherBilk 48. Doris1857, Sept. 19GoldschmidtParis 49. Pales1857, Sept. 19GoldschmidtParis 50. Virginia1857, Oct. 4FergusonWashington 51. Nemausa1858, Jan. 22LaurentNismes 52. Europa1858, Feb. 4GoldschmidtParis 53. Calypso1858, Apr. 4LutherBilk 54. Alexandra1858, Sept. 10GoldschmidtParis 55. Pandora1858, Sept. 10SearleAlbany 56. Melete1857, Sept. 9GoldschmidtParis 57. Mnemosyne1859, Sept. 22LutherBilk 58. Concordia1860, Mar. 24LutherBilk 59. Olympia1860, Sept. 12ChacornacParis 60. Echo1860, Sept. 16FergusonWashington 61. Danae1860, Sept. 9GoldschmidtParis 62. Erato1860, Sept. 14Foerster andBerlinLesser63. Ausonia1861, Feb. 10De GasparisNaples 64. Angelina1861, Mar. 4TempelMa.r.s.eilles 65. Maximiliana1861, Mar. 8TempelMa.r.s.eilles 66. Maia1861, Apr. 9TuttleCambridge, U.S.
67. Asia1861, Apr. 17PogsonMadras 68. Leto1861, Apr. 29LutherBilk 69. Hesperia1861, Apr. 29SchiaparelliMilan 70. Panopea1861, May 5GoldschmidtParis 71. Niobe1861, Aug. 13LutherBilk 72. Feronia1862, May 29Peters andClintonSafford73. Clytie1862, Apr. 7TuttleCambridge 74. Galatea1862, Aug. 29TempelMa.r.s.eilles 75. Eurydice1862, Sept. 22PetersClinton 76. Freia1862, Oct. 21D"ArrestCopenhagen 77. Frigga1862, Nov. 12PetersClinton 78. Diana1863, Mar. 15LutherBilk 79. Eurynome1863, Sept. 14WatsonAnn Arbor 80. Sappho1864, May 2PogsonMadras 81. Terpsich.o.r.e1864, Sept. 30TempelMa.r.s.eilles 82. Alcmene1864, Nov. 27LutherBilk 83. Beatrix1865, Apr. 26De GasparisNaples 84. Clio1865, Aug. 25LutherBilk 85. Io1865, Sept. 19PetersClinton 86. Semele1866, Jan. 14TietjenBerlin 87. Sylvia1866, May 16PogsonMadras 88. Thisbe1866, June 15PetersClinton 89. Julia1866, Aug. 6StephanMa.r.s.eilles 90. Antiope1866, Oct. 1LutherBilk 91. aegina1866, Nov. 4BorellyMa.r.s.eilles 92. Undina1867, July 7PetersClinton 93. Minerva1867, Aug. 24WatsonAnn Arbor 94. Aurora1867, Sept. 6WatsonAnn Arbor 95. Arethusa1867, Nov. 24LutherBilk 96. aegle1868, Feb. 17CoggiaMa.r.s.eilles 97. Clotho1868, Feb. 17CoggiaMa.r.s.eilles 98. Ianthe1868, Apr. 18PetersClinton 99. Dike1868, May 28BorellyMa.r.s.eilles 100. Hecate1868, July 11WatsonAnn Arbor 101. Helena1868, Aug. 15WatsonAnn Arbor 102. Miriam1868, Aug. 22PetersClinton 103. Hera1868, Sept. 7WatsonAnn Arbor 104. Clymene1868, Sept. 13WatsonAnn Arbor 105. Artemis1868, Sept. 16WatsonAnn Arbor 106. Dione1868, Oct. 10WatsonAnn Arbor 107. Camilla1868, Nov. 17PogsonMadras 108. Hecuba1869, Apr. 2LutherBilk 109. Felicitas1869, Oct. 9PetersClinton 110. Lydia1870, Apr. 19BorellyMa.r.s.eilles 111. Ate1870, Aug. 14PetersClinton 112. Iphigenia1870, Sept. 19PetersClinton 113. Amalthea1871, Mar. 12LutherBilk 114. Ca.s.sandra1871, July 23PetersClinton 115. Thyra1871, Aug. 6WatsonAnn Arbor 116. Sirona1871, Sept. 8PetersClinton 117. Lomia1871, Sept. 12BorellyMa.r.s.eilles 118. Peitho1872, Mar. 15LutherBilk 119. Althea1872, Apr. 3WatsonAnn Arbor 120. Lachesis1872, Apr. 10BorellyMa.r.s.eilles 121. Hermione1872, May 12WatsonAnn Arbor 122. Gerda1872, July 31PetersClinton 123. Brunhilda1872, July 31PetersClinton 124. Alceste1872, Aug. 23PetersClinton 125. Liberatrix1872, Sept. 11Prosper HenryParis 126. Velleda1872, Nov. 5Paul HenryParis 127. Johanna1872, Nov. 5Prosper HenryParis 128. Nemesis1872, Nov. 25WatsonAnn Arbor 129. Antigone1873, Feb. 5PetersClinton 130. Electra1873, Feb. 17PetersClinton 131. Vala1873, May 24PetersClinton 132. aethra1873, June 13WatsonAnn Arbor 133. Cyrene1873, Aug. 16WatsonAnn Arbor 134. Sophrosyne1873, Sept. 27LutherBilk 135. Hertha1874, Feb. 18PetersClinton 136. Austria1874, Mar. 18PalisaPola 137. Meliba1874, Apr. 21PalisaPola 138. Tolosa1874, May 19PerrotinToulouse 139. Juewa1874, Oct. 10WatsonPekin 140. Siwa1874, Oct. 13PalisaPola 141. Lumen1875, Jan. 13Paul HenryParis 142. Polana1875, Jan. 28PalisaPola 143. Adria1875, Feb. 23PalisaPola 144. Vibilia1875, June 3PetersClinton 145. Adeona1875, June 3PetersClinton 146. Lucina1875, June 8BorellyMa.r.s.eilles 147. Protogenea1875, July 10SchulhofVienna 148. Gallia1875, Aug. 7Prosper HenryParis 149. Medusa1875, Sept. 21PerrotinToulouse 150. Nuwa1875, Oct. 18WatsonAnn Arbor 151. Abundantia1875, Nov. 1PalisaPola 152. Atala1875, Nov. 2Paul HenryParis 153. Hilda1875, Nov. 2PalisaPola 154. Bertha1875, Nov. 4Prosper HenryParis 155. Scylla1875, Nov. 8PalisaPola 156. Xantippe1875, Nov. 22PalisaPola 157. Dejanira1875, Dec. 1BorellyMa.r.s.eilles 158. Coronis1876, Jan. 4KnorreBerlin 159. aemilia1876, Jan. 26Paul HenryParis 160. Una1876, Feb. 20PetersClinton 161. Athor1876, Apr. 19WatsonAnn Arbor 162. Laurentia1876, Apr. 21Prosper HenryParis 163. Erigone1876, Apr. 26PerrotinToulouse 164. Eva1876, July 12Paul HenryParis 165. Loreley1876, Aug. 9PetersClinton 166. Rhodope1876, Aug. 15PetersClinton 167. Urda1876, Aug. 28PetersClinton 168. Sibylla1876, Sept. 27WatsonAnn Arbor 169. Zelia1876, Sept. 28Prosper HenryParis 170. Maria1877, Jan. 10PerrotinToulouse 171. Ophelia1877, Jan. 13BorellyMa.r.s.eilles 172. Baucis1877, Feb. 5BorellyMa.r.s.eilles 173. Ino1877, Aug. 1BorellyMa.r.s.eilles 174. Phaedra1877, Sept. 2WatsonAnn Arbor 175. Andromache1877, Oct. 1WatsonAnn Arbor 176. Idunna1877, Oct. 14PetersClinton 177. Irma1877, Nov. 5Paul HenryParis 178. Belisana1877, Nov. 6PalisaPola 179. Clytemnestra1877, Nov. 11WatsonAnn Arbor 180. Garumna1878, Jan. 29PerrotinToulouse 181. Eucharis1878, Feb. 2CottenotMa.r.s.eilles 182. Elsa1878, Feb. 7PalisaPola 183. Istria1878, Feb. 8PalisaPola 184. Deiopea1878, Feb. 28PalisaPola 185. Eunice1878, Mar. 1PetersClinton 186. Celuta1878, Apr. 6Prosper HenryParis 187. Lamberta1878, Apr. 11CoggiaMa.r.s.eilles 188. Menippe1878, June 18PetersClinton 189. Phthia1878, Sept. 9PetersClinton 190. Ismene1878, Sept. 22PetersClinton 191. Kolga1878, Sept. 30PetersClinton 192. Nausicaa1879, Feb. 17PalisaPola 193. Ambrosia1879, Feb. 28CoggiaMa.r.s.eilles 194. Procne1879, Mar. 21PetersClinton 195. Euryclea1879, Apr. 22PalisaPola 196. Philomela1879, May 14PetersClinton 197. Arete1879, May 21PalisaPola 198. Ampella1879, June 13BorellyMa.r.s.eilles 199. Byblis1879, July 9PetersClinton 200. Dynamene1879, July 27PetersClinton 201. Penelope1879, Aug. 7PalisaPola 202. Chryseis1879, Sept. 11PetersClinton 203. Pompeia1879, Sept. 25PetersClinton 204. Callisto1879, Oct. 8PalisaPola 205. Martha1879, Oct. 13PalisaPola 206. Hersilia1879, Oct. 13PetersClinton 207. Hedda1879, Oct. 17PalisaPola 208. Lachrymosa1879, Oct. 21PalisaPola 209. Dido1879, Oct. 22PetersClinton 210. Isabella1879, Nov. 12PalisaPola 211. Isolda1879, Dec. 10PalisaPola 212. Medea1880, Feb. 6PalisaPola 213. Lilaea1880, Feb. 16PetersClinton 214. Aschera1880, Feb. 26PalisaPola 215. none1880, Apr. 7KnorreBerlin 216. Cleopatra1880, Apr. 10PalisaPola 217. Eudora1880, Aug. 30CoggiaMa.r.s.eilles 218. Bianca1880, Sept. 4PalisaPola 219. Thusnelda1880, Sept. 20PalisaPola 220. Stephania1881, May 19PalisaVienna 221. Eos1882, Jan. 18PalisaVienna 222. Lucia1882, Feb. 9PalisaVienna 223. Rosa1882, Mar. 9PalisaVienna 224. Oceana1882, Mar. 30PalisaVienna 225. Henrietta1882, Apr. 19PalisaVienna 226. Weringia1882, July 19PalisaVienna 227. Philosophia1882, Aug. 12Paul HenryParis 228. Agathe1882, Aug. 19PalisaVienna 229. Adelinda1882, Aug. 22PalisaVienna 230. Athamantis1882, Sept. 3De BallBothcamp 231. Vindobona1882, Sept. 10PalisaVienna 232. Russia1883, Jan. 31PalisaVienna 233. Asterope1883, May 11BorellyMa.r.s.eilles 234. Barbara1883, Aug. 13PetersClinton 235. Caroline1883, Nov. 29PalisaVienna 236. Honoria1884, Apr. 26PalisaVienna 237. Clestina1884, June 27PalisaVienna 238. Hypatia1884, July 1KnorreBerlin 239. Adrastea1884, Aug. 18PalisaVienna 240. Vanadis1884, Aug. 27BorellyMa.r.s.eilles 241. Germania1884, Sept. 12LutherDusseldorf 242. Kriemhild1884, Sept. 22PalisaVienna 243. Ida1884, Sept. 29PalisaVienna 244. Sita1884, Oct. 14PalisaVienna 245. Vera1885, Feb. 6PogsonMadras 246. Asporina1885, Mar. 6BorellyMa.r.s.eilles 247. Eukrate1885, Mar. 14LutherDusseldorf 248. Lameia1885, June 5PalisaVienna 249. Ilse1885, Aug. 17PetersClinton 250. Bettina1885, Sept. 3PalisaVienna 251. Sophia1885, Oct. 4PalisaVienna 252. Clementina1885, Oct. 27PerrotinNice 253. Mathilde1885, Nov. 12PalisaVienna 254. Augusta1886, Mar. 31PalisaVienna 255. Oppavia1886, Mar. 31PalisaVienna 256. Walpurga1886, Apr. 3PalisaVienna 257. Silesia1886, Apr. 5PalisaVienna 258. Tyche1886, May 4LutherDusseldorf 259. Aletheia1886, June 28PetersClinton 260. Huberta1886, Oct. 3PalisaVienna 261. Prymno1886, Oct. 31PetersClinton 262. Valda1886, Nov. 3PalisaVienna 263. Dresda1886, Nov. 3PalisaVienna 264. Libussa1886, Dec. 17PetersClinton 265. Anna1887, Feb. 25PalisaVienna 266. Aline1887, May 17PalisaVienna 267. Tirza1887, May 27CharloisNice 268.1887, June 9BorellyMa.r.s.eilles 269.1887, Sept. 21PalisaVienna 270.1887, Oct. 8PetersClinton 271.1887, Oct. 16KnorreBerlin -----------------+----------------+---------------+------------
3. Remarks on Table I.
The numbers discovered by the thirty-five observers are respectively as follows:
Palisa 60 Peters 47 Luther 23 Watson 22 Borelly 15 Goldschmidt 14 Hind 10 De Gasparis 9 Pogson 8 Paul Henry 7 Prosper Henry 7 Chacornac 6 Perrotin 6 Coggia 5 Knorre 4 Tempel 4 Ferguson 3 Olbers 2 Hencke 2 Tuttle 2 Foerster (with Lesser) 1 Safford (with Peters) 1 and Messrs. Charlois, Cottenot, D"Arrest, De Ball, Graham, Harding, Laurent, Piazzi, Schiaparelli, Schulhof, Stephan, Searle, and Tietjen, each 1
Before arrangements had been made for the telegraphic transmission of discoveries between Europe and America, or even between the observatories of Europe, the same planet was sometimes independently discovered by different observers. For example, Virginia was found by Ferguson, at Washington, on October 4, 1857, and by Luther, at Bilk, fifteen days later. In all cases, however, credit has been given to the first observer.
Hersilia, the two hundred and sixth of the group, was lost before sufficient observations were obtained for determining its elements. It was not rediscovered till December 14, 1884. Menippe, the one hundred and eighty-eighth, was also lost soon after its discovery in 1878. It has not been seen for more than nine years, and considerable uncertainty attaches to its estimated elements.
Of the two hundred and seventy-one members now known (1887), one hundred and ninety-one have been discovered in Europe, seventy-four in America, and six in Asia. The years of most successful search, together with the number discovered in each, were:
Asteroids.
1879 20 1875 17 1868 12 1878 12
And six has been the average yearly number since the commencement of renewed effort in 1845. All the larger members of the group have, doubtless, been discovered. It seems not improbable, however, that an indefinite number of very small bodies belonging to the zone remain to be found. The process of discovery is becoming more difficult as the known number increases. The astronomer, for instance, who may discover number two hundred and seventy-two must know the simultaneous positions of the two hundred and seventy-one previously detected before he can decide whether he has picked up a new planet or merely rediscovered an old one. The numbers discovered in the several months are as follows: