the Earth is a Solid of Revolution. 207 



the observatory 'at Portsmouth, equal to 9' 42"'91 in time. 

 Let us now compare this quantity with the result of geodeti- 

 cal computation. 



The longitude of Dover has already been calculated in this 

 Journal for September 1828, p. 191 ; viz. 



1° 19'23"-7S east. 

 According to the Survey*, the distance of BeachyHead from 

 the meridian of Greenwich is 9808 fathoms; and the lati- 

 tude being 50° 44-' 21", the longitude will be found equal to 

 15' 15"-02 east: wherefore the difference of longitude between 

 Dover and Beachy Head is 



1° 4' 8"-76. 

 If to this we add 1° 27' 5"-7, which, by former computations,, 

 is the difference of longitude between Beachy Head and Dun- 

 nose, we shall get the difference of longitude between Dover 

 and Dunnose; viz. 



2° 31' 14'H6. 

 According to the Survey f, the distances of the observatory at 

 Portsmouth from the meridian of Dunnose, and from the per- 

 pendicular to the meridian, are respectively 3623 and 11083 

 fathoms. The latitude of Dunnose being 50° 37' 5", the di- 

 stance between the parallels of the two places will come out 

 equal to 11081 fathoms; and as a degree of the meridian at 

 the latitude of Dunnose is 60815 fathoms, we get the difference 

 of latitude equal to 10' 56", and the latitude of the observa- 

 tory equal to 50° 48' 1". Having now the latitude of the ob- 

 servatory and its distance from the meridian of Dunnose, 

 the difference of longitude will be found equal to 5' 38"-45 east- 

 ward. Finally, the difference of longitude between Dover 

 and the observatory will be as follows : 



in arc. in time. 



Geodetically 2° 25' 36" ... 9' 42"'4 



By the chronometers... -^. — ... 9 42 -91 



Diff. ... -51 



The geodetical calculation is probably very near the truth : 

 for if we set aside the two first results which Dr. Tiarks has 

 obtained for the difference of longitude between Portsmouth 

 and Falmouth by his two modes of interpolation, because 

 they are in some degree irregular and different from the rest ; 

 the difference of longitude between Dover and Portsmouth 

 will come out equal to 9' 42"-12, very nearly the same as on 

 the spheroid. According to the Survey the same difference 

 of longitude is 2"-4 less than the quantity found by the chro- 



• Vol. i. p. .307- t Vol. i. p. 3.14. 



nonieters. 



