More and more is man applying science to commerce and industry. When the weather map, which was unknown but little more than half a century ago, indicates the formation of a heavy body of cold air in the extreme northwest, the chief official forecaster at Washington is on the alert; he orders special observations every few hours from the Weather Bureau stations directly within and well in advance of the cold area, and as soon as he becomes satisfied that a cold wave is on its way, the previously arranged system of disseminating warnings is brought into action, and by telegraph, telephone, flags, whistles, bulletins, and other agencies, the people in every city, town and hamlet, and many in the stock and farming regions, are notified of the advancing cold twelve to twenty-four hours before it reaches them. [Illustration: CHART 6.—COLD WAVE ZONES, MARCH TO NOVEMBER. AMOUNT OF FALL AND VERIFYING LIMIT.] Charts 6 and 7 show how the Weather Bureau defines a cold wave. There must be a fall of sixteen degrees, eighteen degrees, or twenty degrees within thirty-six hours and a certain degree of coldness must be reached. The charts show that what is a cold wave in the Gulf region is far from one in the northwest. [Illustration: CHART 7.—COLD WAVE ZONES, DECEMBER, JANUARY, AND FEBRUARY. AMOUNT OF FALL AND VERIFYING LIMIT.] [Illustration: CHART 8.—LOWEST TEMPERATURES IN THE UNITED STATES, 1871-1913.] Chart 8 shows the lowest temperatures experienced in the United States since the founding of the Weather Bureau, 1871 to 1913. Note the influence of the Pacific Ocean in forcing the zero line from Arizona northward to British Columbia. [Illustration: CHART 9.—NUMBER OF COLD WAVES, 1904-1914, INCLUSIVE.] Chart 9 shows the number of times that a cold wave occurred at each station of the Weather Bureau for a period of ten years. The number is greater for northern New England than for the Red River of the North Valley, because practically all the cold waves that cross Minnesota reach New England; and the latter also receives fierce boreal visitors that come to it from the Hudson Bay region lying directly northeast, which do not visit any portion of Minnesota or the region farther west. During the period not a single technical cold wave occurred at the coast stations of California, Oregon, or Washington, while Red Bluff and Sacramento were the only two places in California west of the Sierras, and Roseburg, Oregon, the only station west of the Cascade Range that had any, the numbers being one, two, and five respectively. In the Florida peninsula south of Jacksonville, Tampa had two, while none occurred at Miami. Sometimes the temperature falls lower than that required for a cold wave, but not within the period of twenty-four hours required by the regulations. A notable case in point is the severe cold wave in California in January, 1913, the lowest temperature ever observed being recorded at San Diego on the 7th, when the minimum fell to 25°.