Barometric pressure is not an element of weather, in the ordinary sense of the term, since the fluctuations of pressure that occur in the human environment are entirely inappreciable to the senses. We have seen, however, that pressure is intimately related to wind, which is a weather element of much importance. In noting that systems of high and low pressure are constantly traveling across the country, and that they are accompanied by winds having fairly definite characteristics in relation to each, we have taken an important step toward bringing order out of the (to the uninitiated) chaotic sequence of weather. Obviously, a system of telegraphic weather reports makes it possible to keep close watch of these wind systems, and, from their locations on today's weather map, to form some idea where they will be tomorrow. Thus the weather forecaster is enabled to give notice of the imminence of those violent winds that destroy life and property at sea, and, to a less extent, on land. There is an element of uncertainty in such predictions--since storms, unlike railway trains, are not confined to fixed routes and regular schedules--but the practised forecaster acquires an instinct that helps him to forestall their vagaries. [Illustration: SENDING UP A METEOROLOGICAL BALLOON ON LAKE CONSTANCE Between Switzerland and Germany.] Now what is true of wind is also true to a certain extent of the other elements of weather,--they bear typical relations to the distribution of atmospheric pressure. Cyclones are usually preceded by rising temperature and accompanied by cloudiness and rain or snow; anticyclones are usually preceded by falling temperature and attended by fair weather. Referring again to the map of January 9, 1886, and following the course of the isotherms, or temperature lines, we see that abnormally cold weather prevailed over the Middle Western and Southern States. The isotherm of zero dips far south across northern Texas, Arkansas, Mississippi, Alabama, and Tennessee; while in the upper Mississippi and Missouri Valleys the temperatures were from 20 to 40 degrees below zero. These regions were, in fact, in the grip of a severe "cold wave," which had entered the country a day or two before, preceding the anticyclone here seen central north of Dakota. Cold northwesterly winds were sweeping over the Great Plains, and as far south as the Gulf. [Illustration: HOARFROST Minute crystals of ice deposited from the air. Under a magnifying-glass they show a variety of beautiful forms] The same map shows typical weather accompanying the cyclone central on the Atlantic coast. From the seaboard west to the Mississippi Valley rain or snow had fallen within the previous twenty-four hours (indicated by shading), and snow (indicated by S) was falling at the moment of observation at a majority of stations within this area. Elsewhere in the same region the weather was cloudy.