On the Comparative Level of Lakes and Seas, 333 



of the Red Sea and the Mediterranean, after having occupied the attention 

 of classical antiquity, has been examined in a very general point of view ia 

 Varenius' Treatise on Physical Geography,* for which Newton exhibited 

 so decided a predilection. Anything, however, like accurate measure- 

 ment, was not made previous to the timeof theBVench Expedition to Egypt. 

 The observations conducted by M. Le Pere, have established that the 

 level of the Mediterranean, at the embouchure of the Delta, is inferior by 

 4.1 toises to the neap tides of the Red Sea, near Suez, and 5.1 toises to 

 the level of full tide. It is probable that the cause of this remarkable 

 difference of level is the elevation of the water in the Arabian Gulf to the 

 north of the Strait of Bab- el Man deb, and not, as M. de Corancez t has at- 

 tempted to prove by the hydraulic hypothesis of the reciprocal attrac- 

 tion of the molecules of water, to the deprecsion of the eastern portion of 

 tlie Mediterranean, in which a copious evaporation is not compensated 

 by the volume of water which is poured in by the rivers. 



T/ie Mediterranean and Atlantic. — This comparison of levels, based upon 

 trigonometrical operations, whose precision surpasses all that has hitherto 

 been published in this kind of labour, is two-fold. The former exhibits 

 the almost insensible difference of the Mediterranean and the Atlantic by 

 the Pyrenees; the latter connects the Zuider-Zee, near Amsterdam, 

 with Marseilles. " Delambre had previously endeavoured to deduce from 

 the great chain of triangles which extends from Dunkirk to Barcelona, 

 the levels of the two seas. The triangles included between Rhodez and 

 the Mediterranean gave, for the vertical height of that town, a result 

 which agrees to a fraction of a metre with the height calculated from the 

 ocean, which was deduced from that portion of the chain interposed be- 

 tween Rhodez and Dunkirk. A trigonometrical survey, executed by 

 MM. Coraboeuf, Peytier, Hossard, and Testu, during the years 1825- 

 1827, and running along the southern frontier of France, supplied all 

 that remained doubtful for the solution of the problem. The station 

 of Crabere occupies nearly the middle of the interval which separates 

 the Atlantic from the Mediterranean. Its height has been calculated 

 by three distinct combinations. One has been conducted by proceed- 

 ing from the Atlantic and from the Mediterranean to Crabere, pass- 

 ing by the single series of the summits of the triangles which bound the 

 chain on the south ; a second by selecting exclusively the northern sum- 

 mits ; and the third and last, by taking the diagonal directions, in other 

 words, by taking alternately a northern and a southern summit."t I 

 supply below the results of that combination along the chain of the Py- 

 renees, and of that triangulation which traverses Holland, Germany, and 



♦ Chap. xiii. prop. 5., chap. xv. prop. 8. I will not attempt to justify the ex- 

 aggerated ideas of the author upon the volume of water, which the rivers, and es- 

 pecially the Volga, pour into the Caspian, xvi. prop. 5. 



t Itinfraire d'une partie peu connue dc VAsie mineure, prop. 27. 



X Arago in the Annuaire for 1831, p. 325. Also M^moires present^s & I'Acad, 

 des Sciences, Tom, iii. p. 81. 



VOL. XXXV. NO. LXX. — OCTOBER 1843. Z 



