J)etermination of the Orbits of Comets. 411 



of Feme], and a supposed result so near the truth, it was not 

 difficult to attribute to hazard the success of another operation 

 of a somewhat similar kind. But those who attend to the 

 subject, and whom I am able to convince that Fernel's result 

 was on the wrong side of 54 miles, instead of the right side of 

 69, will perhaps take another look at the mode pursued by 

 Norwood, in which case I am inclined to think they will be 

 able to satisfy themselves, that instead of rowing in the same 

 boat as Fernel, with luck for the steersman, he is well entitled 

 to have his conclusion considered as the result of such skill 

 and patience as could not have led to any other. 



I remain, Gentlemen, yours faithfully, 

 University College, April 2, 1842. A. De Morgan. 



LXII. Inquiry respectitig a correction requisite in the 'working 

 of Dr. Olbers's method of determiniiig the Elements of the 

 Orbits of Comets. By R. Templeton, Esq. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



TTAVING read over with much interest the method of 

 •*- ■*■ determining the elements of the orbits of comets by Dr. 

 Olbers in the last volume of your Magazine for 1835, I se- 

 lected from Lieut. Stratford's Ephemeris of Halley's three posi- 

 tions, intending to familiarize myself with the practical work- 

 ing of the method, but a difficulty met me at the onset. It will 

 be remembered that this comet was detected early in August, 

 when its distance was about twice the radius of the eartl\'s 

 orbit; observations were afterwards made when it was only 

 one-eighth of this quantity, and again when it had nearly ac- 

 quired the same amount. Now in combining these obser- 

 vations, the omission of an allowance for the time elapsed 

 since the comet had actually the positions observed, would in- 

 troduce an error of a quarter of a minute in right ascension, 

 and of half this in declination, which, however small or mo- 

 dified by errors of observation, ought not to be neglected ; I 

 wish in consequence to be informed by some of your Cor- 

 respondents through the medium of your valuable Journal, 

 whether it lias been usual to apply a correction — 8™'l25p 

 to the time of observation after the first approximation adm-its 

 of tolerably accurate values of the curtate distances beino- ob- 

 tained. 



I remain, Gentlemen, yours &c. 

 Colombo, Jan. 26, 1842. R. TempLETON. 



