339 
British Association at Edinburgh, and reviewing the history of 
the principal operations of the kind which have been hitherto 
performed, the author remarks that the Observatory of 
Armagh is unfavorably situated for comparison by signals 
with that of Dublin, though the distance is but sixty-eight 
miles; there being ground about four miles to the south of 
Armagh from 700 to 1200 feet of height; and a ridge from 
600 to 400 feet high, about fourteen miles north of Dublin. 
Lieutenant Larcom investigated all possible stations, giving 
for each its distance and azimuth, and the height above its 
summit to which the signal should be elevated to make it 
visible from both observatories. His help was of essential 
importance; and in consequence of the data supplied by 
him, the station Slieve Gullion was adopted; which is 1893 
feet high, and is distant eighteen miles from Armagh and 
fifty-one from Dublin, . At the latter its summit is a few 
seconds above the boundary of view, but, at the former, so 
much below that boundary, that a height of 800 feet above 
the summit would be required to clear it. Rockets were 
therefore necessary, and on applying for them to the 
Honourable Board of Ordnance, they were supplied from 
Woolwich with the utmost liberality. 
In the operations alluded to above, the rockets (supplied 
by the French Goverment) were what is called 2lbs. and 
carried § oz. of powder; a very great number of them did 
not rise to a sufficient height; and Dr. Robinson thought it 
unsafe to use any of less dimensions. 
The Ordnance also provided tents for the firing party 
and an escort of police was granted by Lieut.-Colonel 
M‘Gregor for their protection, which however proved quite 
unnecessary. 
On the 13th of May they were dispatched to the mountain, 
under the orders of Dr. Robinson’s eldest son, and established 
there in a few hours by the kind aid of the Rey. Dr. Camp- 
bell, Rector of Forkhill, which removed every difficulty ; and 
