the Trigonometrical Operation . 2 gt 
fufficiently near the truth to deferve even the name of an ap- 
proximation. This will inconteftably appear by comparing 
the agronomical refult produced in that way with ours ob- 
tained by actual meafurement on the furface of the earth, and 
angular obfervations of the pole-ftar. Thus, by taking a 
mean of a multitude of the beft of thefe obfervations of 
eclipfes, &c. collected and corrected with great care for the 
purpofe, the difference in time between Greenwich and Paris 
amounts to 9' 30^! *, iilftead of being only 9' 19" nearly, 
which our operation makes it. Now, if the difference in time 
between thefe two Royal Obfervatories was really fomuch, the 
degree of a great circle perpendicular to the meridian in thefe 
latitudes (51° 6 ' 50" that of Goudhurft, or 51 0 T 48^ that of 
the point M, it matters little which of the two is taken) 
would be between 1200 and 1300 fathoms fiiorter than the 
degree of the meridian in the fame latitudes. Hence the 
earth, inftead of being an oblate fpheroid confiderably 
tened at the poles, would be one extremely prolate, in propor- 
tion with regard to the former figure of more than three to 
one, or between 1200 and 1300 — to about 400 + . 
In remote fituations^ fuch as Europe and America, Europe 
and the eaftern parts of Afia, feparated from each other by 
wide oceans, the differences of longitude can only be obtained 
by means of aftronomical obfervations. And as thefe will 
always be liable to fome error, which may be as great on a 
difference of one or two, or a few degrees, as on the whole 
180% it is fufficiently obvious that, to render the effed: of fuch 
* From Dr. Maskelyne’s Paper of 1787, Phil. Tranf. p. 183. it appears, 
that the eclipfes of the ifl Satellite of Jupiter give immediately for the difference 
of meridians of the two Obfervatories (p without being combined with 
obfervations made in other parts of Paris. 
error 
