Page:EB1911 - Volume 18.djvu/290

PHYSICAL DATA] were deduced the following tables, published in the Monthly Weather Review:—

Mean Temperature Gradients in degrees Fahrenheit per 1000 ft. from the ground up to the respective altitudes.

In this table the second column gives the altitude of the ground at the reel on which the kite wire was wound. The third column shows the average gradient in degrees Fahrenheit per 1000 ft. between the reel at the respective stations, and a uniform altitude 5280 ft. above sea-level. The fourth column shows the total reduction to be applied to the temperature at the reel in order to obtain the temperature at the 1 m. level above sea. These gradients and reductions are based upon observations made only during the six warm months from May to October 1898.

The kite-work at the Blue Hill Observatory has been published in full in the successive Annals of the Harvard College Observatory, beginning with 1897, vol. xlii. It has been discussed especially by H. H. Clayton with reference to special meteorological phenomena, such as areas of high and low pressure, fair and cloudy weather, the winds and their velocities at different elevations, insolation, radiation, &c., and has served as a stimulus and model for European meteorologists. Kite-work has also been successfully prosecuted at Trappes, Hamburg, Berlin, St Petersburg, and many other European stations. The highest flights that have been attained have been about 8000 metres.

The great work of L. Teisserenc de Bort began with 1897, when he founded his private observatory at Trappes near Paris devoted to the problems of dynamic meteorology. His results are published in full in the Memoirs of the Central Meteorological Bureau of France for 1897 and subsequent years. Beginning with the sounding balloons devised by Hermite, he subsequently added kite work as supplementary to these. In the Comptes rendus (1904), he gives the mean temperatures as they result from five years of work, 1899–1903, at Trappes. Out of 581 ascensions of sounding balloons there were 141 that attained 14 km. or more, and the following table gives the average temperatures recorded in these ascensions. It will be seen that there is a slow decrease in temperate up to 2 km.; a rapid decrease thence up to 10 km., and a slow decrease, almost a stationary temperature, between

11 and 14 km.; this is the “thermal zone” as discovered and so called by him.

It is evident that the annual average vertical gradient of temperature over Paris is between 4° and 6° C. per 1000 metres of ascent in the free air, agreeing closely with the value 5° per 1000 metres, which has come into extensive use since the year 1890, on the recommendation and authority of Hann, for the reduction of land observations to sea-level. The winter gradients are less than those for summer, possibly owing to the influence of the condensation into cloud and rain during the winter season in France; the same value may not result from observations in the United States, where the clouds and precipitation of winter do not so greatly exceed those of summer. The work at Trappes is therefore not necessarily representative of the general average of the northern hemisphere, but belongs to a coastal region in which during the summer time, at great heights, the air is cooler than in the winter time, since during the latter season there is an extensive flow of warm south winds from the ocean over the cold east winds from the land. Sounding balloons have also been used elsewhere with great success. The greatest heights attained by them have been 25,989 metres at Uccle, Belgium, on the 5th of September 1907, and 25,800 metres at Strassburg, August 1905. The most extensive meteorological explorations of the free atmosphere have been those accomplished in Germany by Richard Assmann and Arthur Berson, beginning (1887) in co-operation with the German Verein for the Promotion of Aeronautics and the Aeronautic Section of the German Army, afterwards under the auspices of the Prussian Meteorological Office, but later as a wholly independent institution at Lindenberg. All the details of the work during 1887–1889 and the scientific results of seventy balloon voyages were published in three large volumes, Wissenschaftliche Luftschiffahrten (Berlin, 1900). The work done at Tegel at the Aeronautical Observatory of the Berlin Meteorological Office, the 1st of October 1899 to April 1905, was published in three volumes of Ergebnisse. But the location at Tegel had to be given up and a new independent establishment, the “Royal Prussian Aeronautic Observatory,” was founded at Lindenberg, under the direction of Dr Assmann, who has published the results of his work in annual volumes of the Ergebnisse of that institution, considering it as a continuation of the work done at Berlin and Tegel. In addition to these elaborate official publications various summaries have been published, the most instructive of which is the chart embodying daily observations with corresponding isotherms at all attainable altitudes, published monthly since January 1903 in Das Wetter. The growth of this aerial work and the reliability of the results may be inferred from a statement of the number of ascensions made each year: 1899, 6; 1900, 39; 1901, 169; 1902, 261; 1903, 481; 1905, 513. This large number, combined with 581 voyages of Teisserenc de Bort at Trappes and many others made in England,