Mr. E. J. Cooper read the following paper on the Deter- 

 mination of Differences of Longitude by means of Shooting 

 Stars. 



" It is not my intention, upon the present occasion, to make 

 any remarks on the various theories that have been published 

 on the subject of what are commonly called shooting stars; I 

 desire merely to lay before the Academy the result of a rough 

 experiment which I recently instituted, to obtain by them 

 differences of longitude between two stations. 



" Artificial signals have been frequently adopted for this 

 purpose, and by none with more perfect success than by my 

 excellent friend, Dr. Robinson, of Armagh. The Academy 

 knows that, to conclude the difference of longitude between 

 Dunsink and Armagh, he obtained rockets from the Ord- 

 nance, which were fired on Slieve Gullion, and the instant of 

 their extinction was noted at the two Observatories. The re- 

 sult was within 0^-03 of that given by the mean of fifteen 

 chronometers belonging to Mr. Dent, the celebrated maker 

 in London. In the year 1841 the difference of longitude was 

 sought in a similar way, between the Observatories of Armagh 

 and Markree. The rockets were fired on Culkagh, but, unfor- 

 tunately, only seven were observed at both places. The result, 

 however, only differed V from that deduced, by the kindness 

 of Captain Larcom, from the Ordnance Survey. 



" It can scarcely be necessary to remind the Academy that 

 these artificial projectiles are not always available for the pur- 

 pose, inasmuch as the height to which they can be made to 

 rise is limited, and there is also a difficulty in securing their 

 sudden extinction. Differences of longitude between places 

 far separated from one another on the earth's surface, cannot, 

 therefore, be decided by their means. 



" I believe that the idea of making shooting stars subser- 

 vient to this end is by no means new ; but I am not aware of 

 its having been carried into practice. They have been ob- 



