340 



though it was very tempestuous, there were fired fourteen 

 rockets on the 14th, thirteen on the 15th, twenty on the 20th, 

 twenty on the 21st, and nine on the 28rd, in all seventy-six. 

 Of these, sixty-three were observed at Armagh, and fifty- 

 three at Dublin, but only forty-two were simultaneous. The 

 explosions were visible to the naked eye at Armagh, and 

 to an ordinary nightglass at Dublin; they were however 

 observed, at the latter, by Sir William Hamilton and Mr. 

 Thompson, his assistant, with the equatorial of five inches 

 aperture, and the dome clock ; at the former by Dr. Robinson 

 with the finder of his great equatorial (two inches three-fourths 

 aperture) and its clock, and by Mr. Edmonson, his assistant, 

 with a telescope (3,2 inches aperture) and the transit clock. 

 A third observer also (but one not much practised) observed 

 them with the west equatorial. 



The time at each observatory was determined by a list 

 of stars previously selected and reduced by the places of 

 Encke's Jahrbuch, so that it is conceived there can be no 

 uncertainty in the work except what arises from the personal 

 equations of the observers, which Dr. Robinson hopes to 

 determine on his way to Birmingham. The numbers of the 

 stars used on each night are stated, and also the probable 

 errors of transit and rocket observations; and the probable 

 mean of the whole work is inferred to give for the difference 

 of longitudes of the two observatories, l m 14 s , 425, exceeding 

 the result of Mr. Dent's chronometers by s , 035. 



The prosecution of these observations was interrupted 

 by the full moon, but the certainty of their result appears 

 sufficient without resuming them. As however there is a 

 mountain in Leitrim where the rockets will be visible at once 

 from Armagh, Dublin, and Mr. Cooper's Observatory of 

 Markree, in Sligo, the determination of the latter apppears 

 sufficiently important to make Dr. Robinson select that 

 station in case of pursuing the matter any further. But it 

 is even more important to cross the Channel. These 21b. 



