{ iio ) 
Latitude was taken with that Inftrument at Dunkerque, 
Paris, and Collioure , and therefore the fouthern Fart 
of the Meridian, containing 6° i8' 5 h fr may be com- 
par’d with the northern Part of it, which contains 2 0 
ii 7 16" and that the former appears to contain more 
Toifes, in Proportion to the Difference of Latitude at its 
Extremities', them the latter. To this may be anfwer’d, 
that, even in this Cafe, the Obfervations made cannot 
be nice enough to determine the Difference of the Length 
of Degrees \ but there is another Error, which might 
corfiiderably miflead the French Gentlemen, and make 
the Degrees appear longer in the South of France ^ that 
the Error in taking the true Height of feveral 
Mountains in Auvergne, Languedoc , and among the 
‘Pyreneans, For if they have allow’d too much for 
the Air’s Refraction (which,by the Obfervations of Tra- 
vellers, is greater towards the northern Regions, and 
diminiihes as we go Southward) the Heights of thofe 
Mountains will be taken too little, and their Bates con- 
fequently longer, which will make the Degrees appear 
bigger than they are. Let A B C D, * for Example, 
be a Mountain, as the Mountain of Rodex , in the La- 
titude of 44 0 21', whofe Height B D is 300 Toifes, 
and whofe Sides A B and B C (fuppos’d to make an 
Angle of 26 0 33', with the Horizon) are found by 
Trigonometry, to be of 670,8 Toifes each •, if by a Mi- 
flake, in taking the Height, it be fuppos’d only equal 
to E D, or 257 Toifes, then the Lines A B and B C 
will become E F and E G fo that the Bafe AC, which 
before was of 1200 Toifes, will become equal to F G, 
which will appear to be 1279,6 Foifes, by Fuel, 47. 
I. Now one fuch Miftakc, in one Degree, will give 
a Difference above twice as great as the fuppos’d Diffe- 
rence 
* Fig. iu- 
