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 2Ist, and nine on the 23rd, 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, 1™ 14°, 425, exceeding 
the result of Mr. Dent’s chronometers by 0°, 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 2lb. 
