26 



places by a comparison of the trae difFerences of the differ- 

 ence of AR. of the B 's enlightened limb on the meridian 

 from one or more stars, with which it has been also com- 

 pared on the same day, under the different meridians, whose 

 longitudinal distances from each other it is required to 

 detei'niine. 



I have, in consequence, made a considerable use of these 

 materials ; and from a number of careful and repeated inves- 

 tigations, I am enabled to decide that this method is capa- 

 ble of the highest degree of accuracy ; is easily put into prac- 

 tice by persons who are furnished with only a good time- 

 keeper, and a portable transit instrument of no very high 

 power or great size; and which, with a simple apparatus, 

 ma}' be set up in a few hours, under even a bell tent or other 

 slight observatory: and from these considerations it appears, 

 that this method is peculiarly adapted to the use of scientific 

 persons, who may chance to be employed on voyages, either 

 of commerce or discovery. When I formerly presented to 

 the Academy a paper on this subject, I was not so well aware 

 of *the practical facility of this method, or of the degree of 

 accuracy, of which it was capable in practice; I spoke and 

 wrote on it, of course, with more diffidence, and as rather 

 suited to the communications of astronomers, in the neigh- 

 bouring 



* I have been strongly confirmed in my opinion of its practical facility by 

 the successful application of a small transit instrument of about six inches focal 

 distance, an achrometic object glass, twenty times mag. power, and system of 

 three par. wires, used occasionally at my glebe residence under a meridian 30* 

 of time E. of the observatory of Armagh. 



