the Trigonometrical Operation . 2 2 5 
gives 26898 for the diftance between the parallels of latitude 
of Greenwich and Dunkirk. 
Because Dunkirk is fituated near the meridian of Paris, the 
diftance between the parallels of latitude of thefe places will be 
nearly equal to what Dunkirk is north from Paris, namely, 
1255173, or 125495 toifes (fee the pages formerly quoted). 
Thefe numbers give respectively 133770 + 26898 ~ 1 60668, 
and 133746.3 + 26898 = 160644,3 fathoms for the diftances 
between the parallels of Greenwich and Paris, a mean between 
which will nearly be 160656 fathoms. 
If therefore the celeftial arc of the meridian between Green- 
wich and Paris is 2° 38' 26", we get 60846 J or 60837 § fa- 
thoms for a degree of the meridian in latitude 50 0 g'f , the 
middle point between Greenwich and Paris ; and a mean of 
* 
thefe two refults 60841 f only exceeds M. Bouguer’s degree 
for the fame latitude about 1 J fathom, a quantity not differing 
fenfibly from the defedf that was brought out by the compu- 
tation in Art. X. Finally, therefore, by taking a mean be- 
tween this and the former length 608385 , wefhall have 60840 
fathoms for the degree of the meridian in latitude 50° f 2 j''\ 
agreeing almoft: exactly with that of M. Bouguer. 
Art. XIV. Comparifon of the length of a degree of a great circle , 
perpendicular to the meridian in Kent , with that in the South 
of France . 
M. Cassini de Thury, in his Book Fa Meridienne neerifee , 
has given us the detail of an operation carried on in the South 
of France in latitude 43 0 32% for the determination of the 
length of a degree of longitude, by marking, at the extremi- 
ties of a long and well afcertained diftance, the inftantaneous 
explofion of gunpowder in the open air. For this purpofe a 
Vol. LXXX. G g Series 
