the Trigonometrical Operation . 205 
For the purpofe of the pole-ftar obfervations a fmall table 
had been previoufly computed, of the exad times of the ftar’s 
being in the eaft and weft ; whence the moments of its greateft 
elongation were readily known. On thefe occafions the Board 
of Longitude’s premium watch, by the late Mr. Harrison, 
was made ufe of. Its rate of going all the time that it was in 
the field in 1787, was very uniformly 9I feconds a day fafter 
than mean time. But in the winter months the watch gra- 
dually changed its rate from plus to minus , and when it wai 
carried into the field in 1788, and, during the five weeks that 
it continued there, it regularly loft on mean time from 3! to 
4 feconds each day ; having in that fhort interim been twice 
compared in Argyll- ftreet, with an excellent clock made by 
Gumming, with an improved Ellxcot’s pendulum. 
With regard to thefe pole-ftar obfervations, whereby the 
differences of longitude, or the angles of convergence of the 
meridians towards each other, have been determined, it is 
neceflary to remark, that although feme few were made to the 
weftward of Greenwich, yet thefe were not at fufficient dis- 
tance from it, and alfo taken of too ihort fides, to afford 
refults that were perfedly fatisfadory and conclufive. It is on 
the obfervations to the eaft ward only, and chiefly on thofe 
made at Goudhurft and Botley Hill, which are upwards of 
twenty-three miles from each other, and reciprocally vifible, 
that we have relied for the fcale of degrees of a great circle 
perpendicular to the meridian in thefe latitudes ; whence thofe 
of longitude have been obtained. The obfervations made at 
Folkftone Turnpike, which is upwards of fifty-eight miles in 
dired diftance from Greenwich, and where, fortunately, the 
double azimuth of the pole-ftar was obtained, are perfedly 
confident with thofe taken at Goudhurft and Botley Hill. But 
when 
