50 OUTLINES OF NATURAL PHILOSOPHY. 



e. The 3d degree, or that which is bisected by the pa- 

 rallel of 4-5, is to be reckoned the most accurate 

 of all, as being deduced from the actual measure- 

 ment of an arch of more than 12 degrees. This 

 arch belongs to the meridian of Paris, which has 

 been continued by the French mathematicians 

 north to Dunkirk, lat. 51 2' 9" N., and south to 

 Formentera, the southernmost of the Balearic isles, 

 in lat. 38 38' 56", the distance being 705188.77 

 toises, (Base Metrique, torn. in. p. 298.) The 

 arch of the same meridian from Dunkirk, till it is 

 intersected by the parallel of Greenwich Observa- 

 tory, lat. 51 28' 39"-|, was also measured by Ge- 

 neral ROY, and found to be 25238.5, or, more 

 exactly, by DE LAMB RE, on applying certain cor- 

 rections, 25241.9 toises. Thus the amplitude 

 of the arch between the parallels of Greenwich and 

 Formentera, is 12 48' 43".5, and the distance 

 730430.67. This arch, however, is not exactly bi- 

 sected by the parallel of 45, Greenwich be- 

 ing 6 28' 39".5 distant from that parallel, and 

 Formentera only 6 20' 3".99. To have the 

 y m length of an arch beginning at Formentera, and ter- 

 minating just as far tothenorth,as Formentera is to 

 the south of 45, we must subtract from the dis- 

 tance of Greenwich the number of toises corres- 

 ponding to 8'35".51, which, as may be inferred 

 from the measurement itself, is 8165.88 toises -, and 

 thus we have 722264.79 for the length of an arch 

 extending 6 20' 3".99 on each side of the paral- 

 lel of 45. 



Now, 



