94 Catalogue of Moon-Culminating Stars, [Feb, 



yj A Catalogue of Stars to be observed with the Moon, in March and 



April, \8ZA,with the view of determining the difference of longitude of the 

 places whereat they may be observed. By John Cumin, Esq. F.R.A.S. 



Of all the methods which have hitherto been devised for the determi- 

 nation of the difference of longitude of any two places on the surface of 

 the earth, it is now agreed on, that that dependent upon the observed 

 interval of time which elapses between the transit of the moon's limb 

 and of a star, having the same declination as the moon, is the most 

 accurate, certain, and expeditious. 



It is the most accurate, because it involves no data but the rate at 

 which the moon's right ascension increases in the interval between its 

 passing over the two meridians : it is the most certain, because it can 

 be put in practice, at least twelve times in each lunation : it is also the 

 most expeditious, because as many stars as may be agreed upon, and as 

 are especially fit for this purpose, may be observed at both observatories 

 on each night ; each of which, if a corresponding one has been made at 

 the other observatory, being independent of the others, serves to give 

 an independent estimate of the longitude. 



It does not seem necessary that I should give a detailed account of 

 this method of determining the longitude, because that has been ably 

 done by Mr. Baily in the Memoirs of the Astronomical Society ; nor 

 that I should insist on the accuracy and value of this method, as both 

 seem to be attested by the fact, that for tbe first time a catalogue of 

 moon -culminating stars has been inserted in the Nautical Almanac for 

 this year : but inasmuch as I have ventured to insert some stars in the 

 accompanying catalogue, which are expressly rejected in the report 

 made by the Committee of the Astronomical Society, relative to the 

 improvements to be introduced into the Nautical Almanac, I feel it 

 necessary to insert here that portion of the report, in order that it may 

 be compared with my reasons for deviating from its implied injunction, 

 and which, I trust, will be deemed sufficient by resident observers in 

 India : 



" The Committee strongly recommend the insertion of the list of mo on -culminating 

 stars, given in the late Supplements to the Nautical Almanac, as affording one of 

 the best modes of determining the longitude of distant places, when the navigator, 

 furnished with a transit instrument, can obtain a landing. As it is absolutely- 

 essential, however, that only one list of such stars should be published for the use 

 of navigators of all nations, and as Professor Encke proposes to discontinue his list 

 as soon as he is assured that the British Government will permanently adopt one, 

 the Committee trust that they may be excused for entering rather more minutely 

 into the mode in which those stars should be selected. They recommend, there- 

 fore, that notmore than four stars should be selected for one day, two of which are to 



