Page:Popular Science Monthly Volume 39.djvu/129

Rh on the distribution of atmospheric pressure not hitherto properlyrecognized, resulting in the mean minimum of pressure being localized distinctly in the south of Iceland—a minimum accompanied by two subordinate minima, one in Davis Strait and the other in the Arctic Ocean, midway between Jan Mayen and the Lofoden Islands. It was made plain, from typical charts giving the mean of four winter months, that one or the other of these minima plays the chief part, the other two being, for the time, subordinate; and that, according as one or the other of the minima predominates, so is the character determined, as regards mildness or severity, of the weather of the winter of the regions surrounding the north Atlantic.

An illustration of his method of working is afforded by the explanation he published of the causes of the cold weather that prevailed over Europe in May, 1874. He showed that a maximum of pressure had prevailed over northwestern and western Europe, "stretching like a great screen" between the Atlantic and central Europe, from Spitzbergen almost to Algiers, while the minimum came partly from the arctic seas, and partly from the western Mediterranean, with gradients steep toward the north and west, Such a distribution of pressure must give rise to a cold polar stream flowing over the greater part of Europe. In Vienna the cold was greatest between the 16th and the 18th, and then the high pressure began to travel eastward, with the production of a great change, so that soon the pressure was lowest in the very district where a few days before the maximum had existed; and the temperature rose. A similar cycle of phenomena occurred in the next month. The author observed in this paper that areas of high pressure are much more quiet and longer lasting than minima, which travel rapidly, change their shapes, and throw off secondary disturbances.

The Meteorological Bulletin had become by the time of Hoffmeyer's death a very important and complete publication. In January, 1884, the number contained pressure results for thirteen stations, temperature for one hundred and nine stations, and rainfalls and other forms of precipitation for one hundred and fiftynine stations; and these results were graphically shown on four maps, accompanied with a full descriptive letterpress—one map giving the isobars for the month, another the isothermals, and on the same map the mean temperature of each of the one hundred and nine stations; a third map, the miminum temperature at each of the stations; while the fourth map gave isohyetal lines, showing the rainfall, with the amount at each of the one hundred and fifty-nine stations entered in plain figures.

The most important results deduced by Hoffmeyer from his maps were contained in his pamphlet, Étude sur les Tempétes de