Page:The National geographic magazine, volume 1.djvu/69

 large extent and deepening intensity of the blue tint, where the temperatures are below the freezing point. From the northwestern to the southeastern portion of the chart we find a difference in temperature of more than 80° F. (from below -10° to above 70°); the steepest barometric gradient is found to the northwest of Block Island, where the pressure varies 1.80 inches in 750 miles (gradient, .036 inch in 15 nautical miles), and .66 inch in 126 miles (Block Island to Albany, N. Y.; gradient, .079). On the chart for 7, March 14th, the depression off Block Island has almost filled up, and the stormy winds have died out and become light and variable, with occasional snow squalls. The other storm center has now regained its ascendency, and is situated about two hundred miles southeast from Sable Island, with a pressure about 29.3. The great wave of low barometer has overspread the entire western portion of the North Atlantic, with unsettled squally weather from Labrador to the Windward Islands. The area of high pressure in advance has moved eastward, to be felt over the British Isles from the 17th to the 21st of the month, followed by a rapid fall of the barometer as this great atmospheric disturbance moves along its circuit round the northern hemisphere. The isotherm of 32° is still south of Hatteras, reaching well out off shore, and thence northward, tangent to Cape Cod, as far as central Maine, and thence eastward to St. Johns, Newfoundland. Great contrasts of temperature and pressure are still indicated, but considerably less marked than on the preceding chart, and the normal conditions are being gradually restored.

The great storm that has thus been briefly described, as well as can be done from the data now at hand and in the limited time at our disposal, has furnished a most striking and instructive example of a somewhat unusual class of storms, and this on such a grand scale, and in a part of the world where the data for its study are so complete, that it must long remain a memorable instance. Instead of a more or less circular area of low barometer at the storm center, there is here a great trough of "low" between two ridges of "high," the whole system moving rapidly eastward, and including "within the arc of its majestic sweep," almost the entire width of the temperate zone. The "trough phenomena," as an eminent meteorologist has called the violent squalls, with shifts