Abstract
IN a paper on the “Marche des Isotherms au Printemps dans le Nord de l'Europe,” Prof. Hildebrandsson of Upsala Meteorological Observatory has struck out a fresh line of inquiry and produced results at once of great scientific and practical value. In a series of five maps he shows the advances with season northwards over North-Western Europe of the isotherms of 32°.0, 37°.4, 42°.8, 48°.2, and 53°.6 respectively, the isotherms being thus 5°.4 (or 3°.0 C.) apart. On January 15 the isotherm of 32°.0 proceeds along the south coasts of the Black Sea and thence westwards to near Lyons, from which point it strikes northwards, passing into the North Sea at Gröningen, and skirts the west of Norway as far as Christiansund. The progress northwards and eastwards of this isotherm at the subsequent fortnightly epochs is extremely instructive, the advance northwards over the plains of Russia being manifoldly more rapid than its advance over the south-west of Norway. By May I the mean temperature of the whole of North-Western Europe has risen above 32°.0 except a small portion from the North Cape to the White Sea. In the height of summer the isotherm of 53°.6 (12° C.) reaches its northern limit, and then includes the whole of Europe except a thin slice of Norway from Vardo to the Lofoden Isles. Since on April 15 this isotherm skirts the southern shores of the Black Sea, its advance northwards is much more rapid than that of 32°.0. Specially instructive is it to note the influence of the various seas and mountain systems on the seasonal advance of the different isotherms. An interesting table is given showing the time taken by various natural phenomena to advance a degree of latitude northwards along the shores of the Baltic. The flowering of plants takes 4.3 days in advancing over a degree of latitude in April, 2.3 days in May, 1.5 days in June, and 0.5 days in July; the ripening of fruits generally 1.5 days; and the fall of forest leaves 2.3 days. Hence the phenomena are propagated with the greatest rapidity when the temperature approaches and reaches the annual maximum.
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Meteorological Notes . Nature 23, 470–471 (1881). https://doi.org/10.1038/023470a0
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DOI: https://doi.org/10.1038/023470a0