422 



THE PHYSICAL GEOGRAPHY OF THE 8EA. 



force with which currents of air or winds would issue under cer- 

 taiu differences of barometric pressure. Under the most favora- 

 ble conditions, i. e., when the places of high and of low barometer 

 are in immediate juxtaposition, as on the inside and outside of an 

 air-pump, an effective difference of 0.006 inch in the barometric 

 pressure would create a breeze with a velocity of seven miles the 

 hour. Such a wind is capable of exerting a horizontal pressure 

 of 0.2 lb. the square foot, thus: 



Changes, however, in the barometer, amounting to five or six 

 times these differences, are observed to take place at sea without 

 producing winds exceeding in velocity the rates above. This is 

 because the places of high and low barometer at sea are far apart, 

 and because, also, of the obstructions to the winds afforded by the 

 inequalities of the earth's surface. 



790. But, in this view of the subject, the importance of a daily 

 Predicting stomw. systcm of wcathcr icports by telegraph on shore, 

 and across the water between Europe and America when the sub- 

 Atlantic cable is well laid, looms up and assumes all the propor- 

 tions of one of the great practical questions of the age. We may 

 conjecture, as the probable result of observation, that the greater 

 the distance between the place of high and low barometer, the less 

 the velocity of wind for a given barometric difference would be. 

 Professor Buys Ballot has discovered, practically, the numerical 

 relation between the force of the wind and given barometric dif- 

 ferences for certain places in Holland. With the view of ascer- 

 taining like relations for this country, it has been proposed to es- 

 tablish a cordon of meteorological stations over the United States, 

 each station being required to report daily to the Observatory in 

 Washington, by telegraph, the height of the barometer, force of 

 wind, etc. By such a plan, properly organized, we might expect 

 soon to be able to give the ships, not only on the great lakes, but 

 in our sea-port towns also, timely warning of many a gale, and to 



