for determining the difference of meridians, &c. 105 
Statement of the method of combining and calculatmg the Obser- 
vations, and obtaining the Rates of the chronometers. 
Previous to stating the result of these observations, it will 
not be irrelevant to explain the method pursued in reducing 
them, and the principles on which the calculation has been 
made ; and it may be here remarked, that the brevity and 
facility of the computations which will appear to be required 
for this purpose, is not the least recommendation of the 
method itself. 
Suppose A and Z to be the two extreme points whose 
difference of longitudes is to be determined, and at each of 
which the true sidereal time is supposed to be known by 
transits of well determined stars and registered by exact 
clocks, or carefully compared chronometers. Intermediate 
between these, suppose two, or any number of stations, 
B, C, &c. chosen, at each of which are placed observers fur- 
nished with telescopes and good chronometers ; and again, 
intermediate between these, and in the order 
A, a, B, b, C, c, Z, 
let posts or stations a, b, c, be selected, at which signals are 
made, by the explosion of gunpowder, the discharge of 
rockets, the extinction of lamps, or otherwise, at regular 
concerted times, and so arranged that the signals at a shall 
be visible from both A and B ; those at b from both B and C ; 
and those at c from B and Z. Now let a signal be made at 
a, and observed both from A and B, and the moment of its 
happening noted at A by the sidereal clock, and at B by the 
P 
MDCCCXXVI. 
