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 :
| Diff. barometric Pressure. | Velocity of Wind. | Horizontal Pressure. | Strength of Wind. |
| .006 inch | 7 miles per hour. | 0.2 lbs. per sq. ft. | Gentle air. |
| 0.010,, | 1-4,,,, | 0.9,,,, | Light breeze. |
| 0.016,, | 21,,,, | 1.9,,,, | Good sailing breeze. |
| 0.06,, | 41,,,, | 7.5,,,, | A gale. |
| 0.14,, | 61,,,, | 16.7,,,, | Great storm. |
| 0.25,, | 82,,,, | 30.7,,,, | Tempest. |
| 0.41,, | 92,,,, | 37.9,,,, | Devastating hurricane. |
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 of the winds afforded by the inequalities of the earth's surface.
790. Predicting storms.—But, in this view of the subject, the importance of a daily system of weather reports 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 proportions 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 differences for certain places in Holland. With the view of ascertaining like relations for this country, it has been proposed to establish 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 send by telegraph to Europe—when one shall be paid—warning of many a one long before it could traverse the Atlantic. The contributions which the magnetic telegraph is capable of making for the advancement
