Dr. Tiarks* account, &c, 
chronometers were accurately determined at Greenwich by 
the Astronomer Royal, and at Falmouth by myself ; and ap- 
plying the means of the rates of each chronometer before 
and after each voyage, as the rate during the voyage, the 
means of all results nearly agreed in giving the longitude of 
Pendennis Castle (the station near Falmouth) 4" (time) 
greater than it is laid down in the Account of the Trigono- 
metrical Survey. Although it thus became very probable 
that some error had crept into the determinations deduced 
from the Survey, still the result of the chronometers, consi- 
dering the manner in which it was obtained, could not be 
looked upon as completely adequate to prove even the exist- 
ence, and much less the amount of an error, which was be- 
fore so little expected. As this question affected however 
the longitude of all places in England determined in the same 
manner as Pendennis Castle, and likewise that of the island 
of Madeira, the difference of longitude of which from Fal- 
mouth had been ascertained, it was resolved to determine 
more accurately, by means of chronometers, the difference of 
longitude between Falmouth and Dover, the latter being a 
station in the Survey easily accessible by sea, and its differ- 
ence of longitude from the former nearly the greatest possible 
in England, viz. more than 6°i. In pursuance of the method 
adopted for this purpose, the chronometers were constantly 
transported from the one place to the other, as soon as the 
time at the former was determined with sufficient accuracy. 
It is clear that in this manner there may be deduced from 
each chronometer two sets of numbers, one for each place, 
representing the difference of the time of the chronometer 
from the mean time of the place at successive moments, and 
MDCCCXXIV. 3 A 
