At great altitudes the air is always very cold, summer and winter. The low temperature may interfere with the efficient working of the engine, and it is, of course, a source of discomfort to the pilot. The formation of ice and heavy deposits of snow lead to inconveniences in both aeroplanes and airships. The pelting of hail is sometimes a painful experience for aeronauts. Lastly, lightning has hitherto left aviators unscathed, but has caused numerous disasters among balloonists. The recent rapid development of aeronautics has laid a heavy burden of additional labor upon the meteorological services of the world, and is producing something like a revolution in their methods. The history of these changes is interesting. From the beginning of the twentieth century until a few years before the World War meteorologists were engaged in a great campaign of upper-air research, utilizing kites, captive balloons, pilot balloons, and sounding balloons to measure the winds, temperature, humidity and pressure at various levels in the atmosphere. In other words, aeronautical methods were employed in the service of meteorology, but the investigators hardly entertained the idea of reversing the relation and making meteorology the handmaiden of aeronautics. The point of view prevailing in those days is well indicated by the fact that the organization that had charge of the upper-air explorations throughout the world was known as the “International Commission for Scientific Aeronautics,” a name that it bore until the year 1919. The plan for providing regular weather reports for the benefit of aeronauts began with some small-scale enterprises in Germany about 1909. In the summer of that year Dr. Franz Linke organized a storm-warning service in connection with the International Aeronautical Exposition at Frankfort, and at the beginning of the year 1911 an aeronautical weather bureau for the whole of Germany was established, with headquarters at the Observatory of Lindenberg. Shortly before the war a similar undertaking was launched in Italy, under Dr. Matteucci, whose service was the first one in the world to publish daily charts, based on telegraphic reports, of the winds at various levels over an entire country.