55 
I had every reason to be satisfied with the result of the mea- 
surements obtained by the chain. I had ordered Mr. Troughton 
to make a theodolite, two feet diameter, although not for the ex- 
press purpose of this survey, yet I had it in contemplation to ob- 
serve with it the large triangles. Mr. Troughton had been much 
engaged, and after waiting a considerable time, I despaired of re- 
ceiving the instrument. The Grand Jury were anxious for the 
progress of the Survey, when I resolyed upon commencing the 
triangulation with a theodolite seven inches diameter, which 
I had intended to use, in combination with the large one, 
and which gave, in observing the three angles of a triangle, a 
difference of not more than one minute, and in many instances 
to thirty seconds. I was not able to observe all the angles of each 
triangle, a proceeding which ought to be strictly attended to in 
all trigonometrical operations; and in the planning of triangles to 
haye them as nearly equilateral as possible. The observations 
from my instrument were not sufficiently minute to warrant any 
spherical correction for the triangles, which I greatly regret; but, 
having so many bases, I possessed the means of verification on all 
sides, and, as will be seen by the map of triangles, was seldom 
doubtful of more than twenty-five feet. Though I am well aware 
that the results of this survey cannot by any means be compared to 
the great operations commenced in England by General Roy, and 
carried on by Colonel Mudge and Major Colby under the Board 
of Ordnance, or to those of France under Delambre, Mechain, 
Arago, and Biot, I am yet inclined to think they may be made 
useful in correcting our maps of Ireland, and that a collection even 
of similar observations would not only be serviceable in improving 
the geography of this kingdom, but is much wanted for the safety 
of the navigator. Asa proof of this, I here subjoin a few observa- 
