476 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



This inclination J is very feeble, but as tbe breadth L of the current 

 of the Gulf Stream is very considerable, the diiference of level between 

 the two borders of the current /i = L tang I attains a considerable value. 

 Thus, let us take as the base of our calculation the figures given by 

 Kiimtz in his Meteorology, or those published more recently by A. D. 

 Bache, Superintendent of the United States Coast Survey. We shall 

 find- 

 First. At the latitude of 26°, between the coasts of Florida and the 

 Bahamas, Z) = 90 kilometers, V = 3 to 4 nautical miles per hour; 

 whence results a difference of level of from 1™.00 to 1".20. 



Second. At the latitude of 33°, between Cape Henlopen, near Charles- 

 ton, and the Bermudas, L = 230 kilometers, V = 2^ nautical miles 

 hourly ; whence results a difference of level of 2.40 meters. 



Third. At the latitude of 42^ south of the Banks of Newfoundland, 

 near the point where the current turns toward the east, L = 470 kilo- 

 meters, V= 1.5 nautical miles hourly; whence we calculate the differ- 

 ence of level to be 3.G0 meters. 



These figures are probably a little too large; the velocity of the cur- 

 rent grows feebler on its borders, and the inclination of the surface of 

 the sea experiences a corresponding reduction. But after all corrections, 

 these data remain important, and we are forced to admit that the 

 surface of the sea, even in an ocean as open as the Atlantic, is not 

 rigorously horizontal; that over very extended regions it presents 

 inclinations that can amount to many seconds, and a level differing 

 from the mean level of the sea by several meters. 



We know that the operations recently conducted for a general level- 

 ing of France have indicated differences between the mean levels of the 

 sea in different parts of the Mediterranean and the Atlantic. It is pos- 

 sible that this singular result ought not to be attributed simply to the 

 complexity of the calculations and the observations, but that it may be 

 the expression of a general fact, and that this fact is explained in part 

 by the general oceanic currents which prevail around the coast. 



(10) Supplementary Note. 



My memoir was addressed to the Academy of Sciences of Paris in 

 the latter part of 1869. Toward the end of the following year, we 

 received a copy of the "Atlas of Storms of the Norwegian Meteorologi- 

 cal Institute" that Mr. Mohn, director of this institute, has done us the 

 honor of presenting to us, and where we find the following lines on 

 page 11: 



"The force of the wind depends on the magnitude of the variation in 

 the pressure of the air experienced from place to place at the surface of 

 the earth, or on the magnitude of the barometric gradient. The greater 

 the variation of pressure from one place to another, the smaller is the 

 gradient and the stronger is the wind. 



" This will be seen upon any one of the charts of this atlas. The 



