Observations on the Comet of Halley. 217 



The agreement between the observed and computed places is as 

 good as had been expected. The errors in latitude, as was fore- 

 seen, are greater than those in longitude ; for the instrument with 

 which the Declinations were measured was graduated only to min- 

 utes ; the Declinations were all taken independently of each other, 

 and at considerable intervals, so that any error in the adjustment of 

 the instrument commonly had a greater influence on the Declinations 

 than on the Right Ascensions. The errors are, however, so small 

 that it was thought useless to attempt to carry the approximation 

 any further. I have taken no account of the planetary perturbations 

 of the comet, and the effect of a resisting medium. Without obser- 

 vations more accurate than my own, this labor would be superfluous. 



The times of perihelion passage, as predicted by five different as- 

 tronomers, were as follows : 



Mr. Lubbock, Oct. 29.7. Paris, M. T. from noon. 



M. Damoiseau, Nov. 3.82. 



Prof. Rosenberger, Nov. 11. 



M. De Pontecoulant, Nov. 12.6. 



Dr. Lehrmann, Nov. 26. 



The date here assigned to Pontecoulant, is that which he has 

 himself given in the Gonnaissance des Tems for 1837. A brief 

 note, however, in L'Institut of Sept. 23, 1835, announces that in 

 that calculation he had employed the value of the earth's mass 

 which is given in the third volume of the Mecanique Celeste, but 

 that in revising his calculation and employing the value of the earth's 

 mass which is now generally received, he found the time of perihe- 

 lion about a day later than before, which makes his final calculation 

 differ but about two days from the truth. 



Halley's comet has made six visits to the sun, at which observa- 

 tions have been made with sufficient accuracy to calculate its orbit. 

 The perihelion passages have been as follows : 



O. S. 1456, June 9. ^ , ^^ ^^ . 



cc iroi A or Interval, /o years, / 7 days. 

 " 1531, Aug. 25. ^ J ^ J 



N. S. 1607, Oct. 26. 



" 1682, Sept. 14. 



" 1759, March 13. 



" 1835, Nov. 16. 



The attractions of the planets, then, have been sufficient to vary 

 the times of revolution, to the amount of nearly two years. Know- 

 VoL. XXX.— No. 2. 28 



