240 
The fundamental formulz employed by Dr. Robinson 
are the following : 
LIE— W+RI; 
Loe’ —w —RY; 
L being the difference of longitudes between an eastern and 
a western station; E the correction of a watch when leaving 
the eastern, and w the correction whenarriving at the western, 
while w’ and £’ are the corrections when leaving the latter 
and returning to the former respectively ; I, 1, the intervals 
of time expended in thus going and returning; and R, R, 
the losing rates corresponding. By supposing R’=R, he 
obtains what he considers the true travelling rate, namely, 
(z’—w’) —(E—W) 
Be pats ite 
and the resulting longitude 
Loi {ek —w+E-—w+R (i—1’)} « 
The errors are then examined to which these determinations 
are liable, and the numerical elements are given, from which 
are deduced fifteen values for the longitude of Armagh, 
varying between the extremes 26™ 34°, 67, and 26™ 36, 32, 
and giving as their general mean, 26" 35°, 44, with a pro- 
bable error less than 0°, 1. 
Eclipses and occultations had given 26" 35%, 47; lunar 
transits, 26" 35%, 64; and a few comparisons, made under 
unfavourable circumstances with a single pocket watch, con- 
structed by the late Mr. Sharp, had appeared to give 26™ 
358, 09. On the whole, Dr. Robinson is not inclined to 
change the quantity which he gave some years ago to Mr. 
Stratford, for insertion in the Nautical Almanac, namely, 
+ 26™ 35°, 50. 
as the west longitude of Armagh from Greenwich. 
The same chronometric comparisons appear to require 
that the value of the longitude of the Dublin Observatory, 
