THE 



LONDON and EDINBURGH 

 PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



OCTOBER 1835. 



XXVIII. On a new Method of reducing Lunar Observations 

 for the Determination of the Longitude. By Charles 

 Rumker, Esq., F.R.A.S.* 



To Lieut.- General Sir Thomas Macdougall Brisbane, K.C.B., 

 F.B.S. L. $ E. 9 F. Ast. S. 9 S?c. 

 Sir, 

 r | 1 HE lively interest which you took in the determination of 

 ■■•' the longitude by lunars, and the success which attended 

 your observations, prompt me to propose to you the following 

 method of their reduction, which admits of greater accuracy 

 when either altitude is low. Already when I had the honour 

 of accompanying you on your passage to New South Wales, I 

 had an opportunity of remarking the necessity of a more cor- 

 rect allowance for the refraction of the lower object. This 

 subject has since been resumed by a celebrated astronomer, 

 whose method appears to me, however, not likely to be ge- 

 nerally adopted by seafaring men, requiring, moreover, a par- 

 ticular ephemeris, which becomes inapplicable under ordinary 

 circumstances, where the usual methods are sufficiently cor- 

 rect. I trust, therefore, that the following method, which re- 

 quires no other ephemeris than the Nautical Almanac, and 

 may, as circumstances require, be computed with more or less 

 precision, will be found of more practical utility. 



The object of the present lines is the correction of the error 

 committed in the usual methods of clearing the apparent di- 

 stance between sun and moon by taking out the refractions 



* Communicated by Sir T. M. Brisbane, K.C.B. &c. 

 Third Series. Vol. 7. No. 40. Oct. 1835. 2 I 



