332' On the Gomparati'ec Level of Lakes and Seas, 



bility, long a^o established by ]\I. Letronne, of the non-communlcatioil 

 of the Jordan, in historic times, with the Elanitic gulf of the Red Sea. . 

 If the depression of the Caspian Sea and of the surrounding country is 

 inconsiderable, in comparison of the barometrical and trigonometrical 

 measurements made in Palestine, and which, numerically, seem to be 

 very near the truth, it, on the contrary, gains in importance when com- 

 pared with the diiferences presented by the different parts of the ocean 

 which are in free communication with each other. In the sequel, in the 

 way of comparison, I shall cite those only which are based on gcodsesi- 

 cal levelling, which are altogether worthy of confidence. 



The Gulf of Mexico (Mer des Antilles) and the Pacific Ocean. 



General Bolivar, at my request, in the years 1828 and 1829, engaged 

 the services of an officer of his ^taff, Mr Lloyd, an American, and of M, 

 Falmarc, a Swede, carefully to survey the isthmus of Panama. In this 

 operation they employed a levelling telescope of Carey's. At the mouth 

 of the Uio Chagres, in the Gulf of Mexico, the difference of the elevation 

 at the full and ebb tide was only 0.16 of a toise ; at Panama, on the shores 

 of the Pacific Ocean, it was 3.3 toises. From the surve}' of Messrs 

 Lloyd and Palmare, it results that the mean level of the Pacific Ocean* is 

 at the most but 0.54 of a toise more elevated than the water of the Gulf 

 of Mexico, but at the time of the neap tide upon the two coasts, the Pa- 

 cific Ocean is lower than the Gulf of Mexico, to the extent of 1.01 toises. 

 At different hours of the day, then, it is now the one sea, and now the 

 other that is highest. M. Arago has accurately observed, that, in an un- 

 cultivated country, beset with difficulties, in going over a line of 33 

 leagues, and taking 935 observations, the small error of three feet may 

 readily occur ; and, consequently, that every proof exists that the differ- 

 ence of level between the two great seas, which communicate by the 

 Straits of Magellan round Cape Horn, is so small as to be inappreciable.f I 

 myself believe that I established, by means of barometrical observations 

 taken from 1799 to 1804, and corrected from the effects of hourly vari- 

 ations, that if any sensible difference existed between the waters of the 

 Mexican Gulf and the Pacific Ocean, this difference was probably not 

 more than three 3'ards (metres). My barometrical observations, J as well 

 as the comparison of those of M. Boussingault in 1822 at La Guayra, 

 and those of M. Pentland at Callao of Lima, in 1826, seem to assign even 

 a lower level to the waters of the Mexican Gulf; but the variable influence 

 of capillarity throws a doubt upon the obtained results where they refer 

 to the decimals of millimetres in the column of mercury. 



The Mediterranean and the lied Sea. — The problem of the relative height 



* Philos. Transact., 1830, p. 84. 



t Notices Scientijiqucs of M. Arago, in the Annuairc for 1831, p. 319. 

 :|: Humboldt, Jiehtion ffiet. T. iii., p. 355-7, Arago, in les Ann. de Chimle, T. i. 

 p, 55 and 64. 



