It has also diminished in apparent magnitude, and the light has changed from a strong yellowish-white to a dull bluish-gray color. "The tabular order of the mean relative magnitudes of the satellites is, third, fourth, first, second. "One of the most remarkable features attending the progress of this phenomenon was the rapidity with which the change from bright to dark took place. At 9h 15m there was no indication of change, unless the apparent gradual fading of the light of the satellite is so considered, but which I should rather attribute to the increased amount of light reflected from Jupiter nearer this centre. At 9h 18m 30, when I again saw the satellite, the dark part had so increased as not to be mistaken for a moment, and my son represents the change as taking place almost instantaneously, not leaving a doubt from the first. "The satellite was watched for some time after the transit, and it appeared to be gradually resuming its pristine brilliancy." Mr. Mitchell read the subjoined account of a remarkable meteor, which was seen from Nantucket, on the 6th of March last. "On the 7th of last month (March), 1848, while in Boston, I received a letter from my daughter, at Nantucket, stating that on the previous morning, at about half past two o'clock, a meteor of surpassing magnitude and brilliancy was seen by several persons, and its report was so loud that many individuals were awakened by it. With a view of eliciting information from other quarters, I requested the editor of the Evening Transcript to give publicity to the fact, simply as I have now stated it. "On returning to Nantucket, so much was said of the magnitude and extreme brightness of the meteor, and of the loudness of the report, that I was induced to make a systematic investigation of the cir cumstances attending it, in view of the possibility that some of the fragments, or the undivided body itself, might have fallen upon the island. "Among the witnesses of the phenomenon were two of the street watchmen, both intelligent men, who were situated, at the moment, 3,250 feet asunder, and in a direction from each other nearly at right. angles with the direction of the meteor as first seen. With each of these gentlemen I went to the spot which they respectively occupied when they first saw it, and by the aid of buildings in the vicinity I was able to ascertain, to tolerable satisfaction, the apparent direction of its motion, and its position when earliest seen. Taking afterwards, by means of a circumferenter, the difference of its apparent position at these extreme points, and assuming that the eyes of both observers were directed to it at the same moment, which is the more likely to be true, from the fact, that they were both facing the region occupied by the meteor, I found its parallax with this base to be 60; its direction from one being south 5210 east, and from the other south 464° east, each at an estimated altitude of 30°. "The report occurred ninety-two seconds after the entire extinction of the illumination, and after the meteor, without any appearance of separation, had reached the horizon. "To obtain the measurement of this interval, I requested each watchman separately, and without the knowledge of the other, to move onward in his usual pace to the position at which he had arrived when the report was heard, and during this period, I noted the time by a chronometer; and it is certainly remarkable, that by this rude method they differed from each other less than five seconds. "All parties agree that the illumination was quite equal to that of a bright moon, giving to every visible object a frightful aspect; and also that the brilliancy of the meteor was extremely painful to the eye. Only two persons with whom I have conversed were so situated as to follow its course quite to the horizon, or near to the point of its contact with the earth. Those individuals testify, that it emitted no scintillations, but maintained a perfectly circular form through its whole The report is said to have been startling; the rattling of windows and jarring of the houses are spoken of by many witnesses, every one noticing that, unlike the discharge of cannon or a peal of thunder, it was without reverberation. Some persons who were roused by the extreme light, but did not see the illumination, supposed it to have been the jar of an earthquake. course. "Observers differ widely in estimating its apparent diameter, though they were requested to observe the moon as the standard of measure. ment. Some supposed it exceeded the moon; others, and quite the greatest number, thought it less than the moon in apparent diameter, the lowest estimate being two thirds the disk of that luminary. I take twenty minutes to be the optical apparent diameter of the meteor; stripping this of all possible illusion arising from its dazzling brightness, I am persuaded that it subtended an angle of at least twelve minutes. "From these data, rude and imperfect as they necessarily are, I conclude that a mass of matter nearly spherical, one hundred and five feet in diameter, entered the earth's atmosphere in a direction from west to east, passed the town of Nantucket, with great obliquity, at the distance of nearly 6 miles, and impinged upon the earth's surface 192 miles east of the town, in the Atlantic ocean, 14 miles east of the island. "Whether this mass was solid or fluid is uncertain; and yet we can hardly suppose that a gaseous body, when rushing through the atmosphere, would have maintained so constantly its globular form, as indicated by its circular appearance; nor are we prepared to admit, that one liquid mass impinging on another would produce a report, which, at the distance of twenty miles, would be so sharp and jarring, that many persons should think it an earthquake. My own opinion is, formed from evidence of which the foregoing is a mere brief, that a solid mass of matter, of no inconsiderable size, fell upon the earth on that occasion." Professor Peirce communicated the following letter from Mr. Sears C. Walker to himself. "Washington, D. C., March 6th, 1848. "I have computed the small corrections of the elliptic elements of the planet Neptune, which you were so kind as to communicate to the American Academy in December last. These corrections, applied to the first approximation, furnish the second approximation towards the elliptic elements of Neptune. M328° 32' 44".20, mean noon, Greenwich, Jan. 1, 1847. T164.6181 tropical years. "The ephemeris from these elements II., after applying the values of the perturbations § v and 8 r, from your paper of Dec. 17th, 1847, before referred to, requires, in order to conform to observation, the following corrections in R. A. and Dec. The agreement is so close, that I shall not attempt any farther approximation towards the true elements till after the next opposition has been observed. For the Lalande observations, I have used Mauvais's places from the Comtes Rendus. They furnish internal evidence of their excellence, by their perfect representation of the two days' motion of the planet. "Yours, truly and respectfully, "SEARS C. WALKER." Professor Peirce communicated a memoir from Mr. G. P. Bond, on the direct computation of the orbit of a comet, from three observations of its right ascension and declination, and remarked upon the clear and simple views which Mr. Bond had taken of the subject. Professor Peirce announced that he had completed his investigation into the action of Neptune upon Uranus, and had ascertained that this planet will completely account for the observed irregularities in the motions of Uranus, provided that mass of Neptune is adopted which is derived from Mr. Bond's observations of Lassell's satellite. "The following table exhibits the residual differences between the observed and computed longitudes of Uranus, from which it appears that, with the mass of Neptune deduced from Mr. Bond's observations of Lassell's satellite, the theory of Uranus is now perfect, and the motions of this planet do not indicate that there is any other unknown source of perturbation. It appears, moreover, that the mass which is Ancient. derived from Mr. Bond's observations is far more satisfactory than that which M. Struve has obtained from his own observations. "The fifth and sixth columns of the table contain the small discrepancies between theory and observation which would have remained after making allowance for the action of the hypothetical planets of Adams and Leverrier; and their comparison with the second column shows that the observation of 1690 was not sufficiently well represented by the theories which resulted in the discovery of Neptune. "The seventh column contains the residual defects of the best theory of Uranus, which is independent of the action of an external planet, and is the true basis of the researches of Adams and Leverrier. This theory was constructed by Leverrier from all the modern observations, and the discrepancy between theory and observation was the final proof that Uranus was subjected to some unknown cause of perturbation. The time t is the number of Julian years from Jan. 1, 1850. The longitude of the perihelion is denoted by , with the symbol of the planet subjacent. "Residual Differences between the Theoretical and Observed Longitudes of Uranus, from the Theories of Peirce, Leverrier, and Adams. Date. for its mass,-- From Peirce's Theory of Neptune, adopting From Lever From Ad- From Lever- = 1981 – 1st so lite mass 14196 = 9322 = 666 el. |
