42 LEVELS OF THE ATLANTIC AND PACIFIC 



that the influence of westward pressure in raising a 

 current tide on the eastern side of the Isthmus, and 

 depressing the water on the western side, must, ac- 

 cording to our theory, immensely preponderate over 

 any possible effects of evaporation which cannot do 

 more than cause a trivial increase or decrease in the 

 difference of level which would result from the sole 

 action of westward pressure. Nor does it appear to 

 us possible that among all the forces hitherto known 

 and recognised as acting upon the ocean and atmo- 

 sphere, there can be any counteracting influence 

 sufficiently powerful to prevent the action of west- 

 ward pressure from actually causing the level of the 

 Atlantic to be higher than that of the Pacific about 

 the Isthmus of Panama. 



189. Notwithstanding this, we find it stated in 

 Lippincott's Geographical Dictionary that, i the mean 

 level of the Pacific, as ascertained by measurements 

 taken in the Bay of Panama and the Gulf of Mexico, is 

 supposed to be 3^ feet above that of the Atlantic.' 

 And when we consider that, according to the argu- 

 ments contained in vol. i., the magnetic needle, when 

 placed at the south magnetic pole, pointing right 

 away into space, marks the point in space towards 

 which the earth is moving; and the Pacific shore of 

 the Isthmus of Panama, lying almost at right angles 

 to the direction of that motion, receives the full force 

 of the northward pressure caused in the South Paci- 

 fic by that motion : then the fact above mentioned 



