H ALLEY 8 COMET. 



methods of investigation were still further improved ; and, above 

 all, the number of observers was greatly augmented. Before the 

 epoch of its return in 1835, its motions, and the effects produced 

 upon them by the disturbing action of the several planets, were 

 computed by MM. Damoiseau, Pontecoulant, Rosenberger, and 

 Lehmann, who severally predicted its arrival at perihelion : 



Damoiseau . . .4th Nov. 1835. 

 Pontecoulant . . . 7th ,, 



Kosenberger . . . llth ,, 

 Lehmann . . . . 26th ,, 



62. These predictions were all published before July, 1835. 

 The comet was seen at Rome on the 5th August, in a position 

 within one degree of the place assigned to it for that day, in the 

 ephemeris of M. Rosenberger. On the 20th August, it became 

 visible to all observers, and pursued the course with very little 

 deviation, which had been assigned to it in the ephemerides, 

 arriving at its perihelion on the 16th Nov., being very nearly a 

 mean between the four epochs assigned in the predictions. 



After this, passing south of the equator, it was not visible in 

 northern latitudes, but continued to be seen in the southern 

 hemisphere until the 5th of May, 1836, when it finally disappeared, 

 not again to return until the year 1911. 



63. A synoptical Table of the elements of the orbit of this 

 comet, deduced from the observations made on each of its seven 

 successive returns to perihelion, between 1378 and 1835 in- 

 clusive, may be seen by a reference to the " Hand-Book of 

 Astronomy." 



It appears that the mean distance of this comet is about 

 eighteen times that of the earth, and that it is consequently at a 

 little less than the mean distance of Uranus. "When in peri- 

 helion, its distance from the sun is about half the earth's 

 distance, while its distance in aphelion is above thirty-five times 

 the earth's distance, and therefore seventy times its perihelion 

 distance. 



64. On the 20th of July, 1812, a comet was discovered by 

 M. Pons, whose orbit was calculated by Professor Encke, and was 

 found to be an ellipse of such dimensions as to give a period of 

 75| years, equal to that of Halley's comet. 



65. On the 6th of March, 1815, Dr. Olbers discovered at 

 Bremen, a comet whose orbit, calculated by Professor Bessel, 

 prcrved to be an ellipse, with a period of 74 years. The next 

 perihelion passage of this comet is predicted for the 9th of 

 February, 1887. 



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