II. Account of some circumstances historically connected with the discovery of the planet exterior to Uranus. (Read by the Astronomer Royal.) It has not been usual to admit into the memoirs of this society mere historical statements of circumstances which have occurred in our own times. I am not aware that this is a matter of positive regulation: it is, I believe, merely a rule of practice, of which the application in every particular instance has been determined by the discretion of those officers of the society with whom the arrangement of our memoirs has principally rested. And there can be no doubt that the ordinary rule must be a rule for the exclusion of papers of this character, and that, if a positive regulation is to be made, it must absolutely forbid the presentation of such histories. Yet it is conceivable that events may occur in which this rule ought to be relaxed; and such, I am persuaded, are the circumstances attending the discovery of the planet exterior to Uranus. In the whole history of astronomy-I had almost said in the whole history of science-there is nothing comparable to this. The history of the discoveries of new planets in the latter part of the last century, and in the present century, offers nothing analogous to it. Uranus, Ceres, and Pallas, were discovered in the course of researches which did not contemplate the possible discovery of planets. Juno and Vesta were discovered in following up a series of observations suggested by a theory which, fruitful as it has been, we may almost venture to call fanciful. Astræa was found in the course of a wellconducted re-examination of the heavens, apparently contemplating the discovery of a new planet_as only one of many possible results. But the motions of Uranus, examined by philosophers who were fully impressed with the universality of the law of gravitation, have long exhibited the effects of some disturbing body: mathematicians have at length ventured on the task of ascertaining where such a body could be; they have pointed out that the supposition of a disturbing body moving in a certain orbit, precisely indicated by them, would entirely explain the observed disturbances of Uranus: they have expressed their conviction, with a firmness which I must characterize as wonderful, that the disturbing planet would be found exactly in a certain spot, and presenting exactly a certain appearance; and in that spot, and with should do wrong if we considered that these two persons alone are to be regarded as the authors of the discovery of this planet. I am confident that it will be found that the discovery is a consequence of what may properly be called a movement of the age; that it has been urged by the feeling of the scientific world in general, and has been nearly perfected by the collateral, but independent labours, of various persons possessing the talents or powers best suited to the different parts of the researches. Without pretending to fix upon a time when the conviction of the irreconcilability of the motions of Uranus with the law of gravitation first fixed itself in the minds of some individuals, we may without hesitation date the general belief in this irreconcilability from the publication of M. Alexis Bouvard's Tables of Uranus, in 1821. It was fully shown, in the introduction to the tables, that, when every correction for perturbation indicated by the best existing theories was applied, it was still impossible to reconcile the observations of Flamsteed, Lemonnier, Bradley, and Mayer, with the orbit required by the observations made after 1781: and the elements of the orbit were adopted from the latter observations, leaving the discordances with the former (amounting sometimes to three minutes of arc) for future explanation. The orbit thus adopted represented pretty well the observations made in the years immediately following the publication of the tables. But in five or six years the discordance again growing up became so great that it could not escape notice. A small error was shown by the Kremsmünster Observations of 1825 and 1826: but, perhaps, I am not in error in stating that the discordance was first prominently exhibited in the Cambridge Observations, the publication of which from 1828 was conducted under my superintendence. While still residing at Cambridge, I received from the Rev. T. J. Hussey (now Dr. Hussey) a letter, of which the following is an extract: z= A = 305° 6' 35' rb sin (B + »); log. b = B: = 217° 29′ 5′′ 9,97440; rc sin (C+); log. c = 9.54802; C = 197° 1' 46' II. Account of some circumstances historically connected with the discovery of the planet exterior to Uranus. (Read by the Astronomer Royal.) It has not been usual to admit into the memoirs of this society mere historical statements of circumstances which have occurred in our own times. I am not aware that this is a matter of positive regulation: it is, I believe, merely a rule of practice, of which the application in every particular instance has been determined by the discretion of those officers of the society with whom the arrangement of our memoirs has principally rested. And there can be no doubt that the ordinary rule must be a rule for the exclusion of papers of this character, and that, if a positive regulation is to be made, it must absolutely forbid the presentation of such histories. Yet it is conceivable that events may occur in which this rule ought to be relaxed; and such, I am persuaded, are the circumstances attending the discovery of the planet exterior to Uranus. In the whole history of astronomy-I had almost said in the whole history of science there is nothing comparable to this. The history of the discoveries of new planets in the latter part of the last century, and in the present century, offers nothing analogous to it. Uranus, Ceres, and Pallas, were discovered in the course of researches which did not contemplate the possible discovery of planets. Juno and Vesta were discovered in following up a series of observations suggested by a theory which, fruitful as it has been, we may almost venture to call fanciful. Astræa was found in the course of a wellconducted re-examination of the heavens, apparently contemplating the discovery of a new planet as only one of many possible results. But the motions of Uranus, examined by philosophers who were fully impressed with the universality of the law of gravitation, have long exhibited the effects of some disturbing body: mathematicians have at length ventured on the task of ascertaining where such a body could be; they have pointed out that the supposition of a disturbing body moving in a certain orbit, precisely indicated by them, would entirely explain the observed disturbances of Uranus: they have expressed their conviction, with a firmness which I must characterize as wonderful, that the disturbing planet would be found exactly in a certain spot, and presenting exactly a certain appearance; and in that spot, and with should do wrong if we considered that these two persons alone are to be regarded as the authors of the discovery of this planet. I am confident that it will be found that the discovery is a consequence of what may properly be called a movement of the age; that it has been urged by the feeling of the scientific world in general, and has been nearly perfected by the collateral, but independent labours, of various persons possessing the talents or powers best suited to the different parts of the researches. It Without pretending to fix upon a time when the conviction of the irreconcilability of the motions of Uranus with the law of gravitation first fixed itself in the minds of some individuals, we may without hesitation date the general belief in this irreconcilability from the publication of M. Alexis Bouvard's Tables of Uranus, in 1821. was fully shown, in the introduction to the tables, that, when every correction for perturbation indicated by the best existing theories was applied, it was still impossible to reconcile the observations of Flamsteed, Lemonnier, Bradley, and Mayer, with the orbit required by the observations made after 1781: and the elements of the orbit were adopted from the latter observations, leaving the discordances with the former (amounting sometimes to three minutes of arc) for future explanation. The orbit thus adopted represented pretty well the observations made in the years immediately following the publication of the tables. But in five or six years the discordance again growing up became so great that it could not escape notice. A small error was shown by the Kremsmünster Observations of 1825 and 1826: but, perhaps, I am not in error in stating that the discordance was first prominently exhibited in the Cambridge Observations, the publication of which from 1828 was conducted under my superintendence. While still residing at Cambridge, I received from the Rev. T. J. Hussey (now Dr. Hussey) a letter, of which the following is an extract: as might have been expected, it had occurred to him, and some correspondence had taken place. between Hansen and himself respecting it. Hansen's opinion was, that one disturbing body would not satisfy the phenomena; but that he conjectured there were two planets beyond Uranus." tion of the astronomers of Paris was directed to Uranus. Although no allusion is made in the last letter (M. E. Bouvard's) to the possible disturbing planet, it would be wrong to suppose that there was no thought of it. fact, during the whole of these efforts for reforming the tables of Uranus, the dominant thought In My answer was in the following was, "Is it possible to explain terms: the motions of Uranus, without admitting either a departure from G. B. Airy to Rev. T. J. Hussey. the received law of attraction, [EXTRACT.] "Observatory, Cambridge, "I have often thought of the irregularity of Uranus, and since the receipt of your letter have looked more carefully to it. It is a puzzling subject, but I give it as my opinion, without hesitation, that it is not yet in such a state as to give the smallest hope of making out the nature of any external action on the planet. Flamsteed's observations I reject (for the present) without ceremony: but the two observations by Bradley and Mayer cannot be rejected. Thus the state of things is this-the mean motion and other elements derived from the observations between 1781 and 1825 give considerable errors in 1750, and give nearly the same errors in 1834, when the planet is at nearly the same part of its orbit. If the mean motion had been determined by 1750 and 1834, this would have indicated nothing: but the fact is, that the mean motions were determined (as I have said) independently. This does not look like irregular perturbation." The astronomer royal then read a letter from M. Eugène Bouvard, showing how vigorously the atten or the existence of a disturbing planet?" I know not how far the extensive and accurate calculations of M. Eugène Bouvard may have been used in the subsequent French calculations, but I have no doubt whatever that the knowledge of the efforts of M. Bouvard, the confidence in the accuracy of his calculations, and the perception of his failure to reconcile in a satisfactory way the theory and the observations, have tended greatly to impress upon astronomers, both French and English, the absolute necessity of seeking some external cause of disturbance. Several months before the date of the last letter quoted, I had received the first intimation of those calculations which have led to a distinct indication of the place where the disturbing planet ought to be sought. Professor Challis to G. B. Airy. [EXTRACT.] "Cambridge Observatory, "A young friend of mine, Mr. Adams, of St. John's College, is working at the theory of Uranus, and is desirous of obtaining errors of the tabular geocentric longitudes of this planet, when near opposi |