Proceedings of the American Academy of Arts and Sciences. RESULTS OF THE FRANCO-AMERICAN EXPEDITION TO EXPLORE THE ATMOSPHERE IN THE TROPICS. BY A. LAWRENCE ROTCH. RESULTS OF THE FRANCO-AMERICAN EXPEDITION TO EXPLORE THE ATMOSPHERE IN THE TROPICS. BY A. LAWRENCE ROTCH. Presented February 14, 1906. Received September 13, 1906. It has long been believed that the ascending currents above the thermal equator proceed immediately over the northeast and southeast trade-winds as southwest and northwest anti-trades. It is possible that part of the anti-trade sinks down over the high barometric pressure in the North and South Atlantic oceans and returns with the trade-winds, but the greater portion descends north and south of the origin of the trades and continues to the poles as the prevailing southwest or northwest winds of the North and South Temperate zones, respectively. The facts upon which this theory is based, as regards the Atlantic Ocean, are mainly observations upon the Peak of Teneriffe, where the southwest wind can be observed the whole year; and although it is lower in winter than in summer, there are no observations which prove that this anti-trade ever reaches the surface of the ocean. The author, after he had made the first meteorological observations over the ocean, with kites flown from a transatlantic steamer in 1901, concluded that a vessel, which could be navigated at will, would enable meteorological data to be obtained with kites independently of the natural wind.1 He suggested the application of this method to the exploration of the atmosphere in the trade-wind region at the Glasgow meeting of the British Association in 1901,2 and at the Berlin Congress for Scientific Aëronautics in 1902.3 In order to organize such an expedition, applications for aid were addressed in 1902 to the Prince of Monaco, and in 1903 to the Carnegie Institution, but without receiving the desired assistance. However, Professor Hergesell, President of the International Commission for Scientific Aeronautics, succeeded in interesting the Prince of Monaco in the scheme, 1 Science, 14, 412 and 896. * Report Brit. Ass. Adv. Sci., Glasgow, 1901, Transactions Section E. 3 Protokoll der 3. Versammlung der Internationalen Kommission für wissenschaftliche Luftschiffahrt, Beilage 11. and upon his yacht, the "Princesse-Alice," during the summer of 1904, kite-flights were made in the region bounded by Spain, the Azores, and the Canaries. Although a height exceeding that of the Peak of Teneriffe was attained several times, the southwest current, which had been reported on this mountain, was not found. Thereupon Professor Hergersell stated that he believed this current was due to the disturbing influence of the island, and that in the region explored the interchange of air takes place through the northwest current, which he had observed.4 These conclusions, which involved a fundamental principle of meteorology, namely, the existence of the upper return-trades, seemed to demand further investigation, and accordingly M. Teisserenc de Bort and the writer undertook to execute this through their assistants, Messrs. Maurice of Trappes Observatory and Clayton of Blue Hill Observatory. Mr. Clayton made the voyage from Boston to Gibraltar, via the Azores, in June, 1905, on the White Star steamer "Romanic," and flew kites six times to an average height of about 1000 meters. The steam-yacht "Otaria," of 350 tons, purchased and equipped by M. Teisserenc de Bort for exploring the atmosphere, and having on board Messrs. Maurice and Clayton as the scientific staff, went during the months of July and August, 1905, at the mutual expense of her owner and the writer, from the Mediterranean, via Madeira, the Canary and Cape Verde islands, to latitude 10° north, longitude 30° west, returning via the Azores and Corunna (Spain) to Havre. Seventeen kite-flights were made over the ocean besides two in the harbor of Santa Cruz (Teneriffe) to study the sea-breeze, and another off Corunna (Spain) during the total solar eclipse of August 30, 1905. In this way continuous records of barometric pressure, air-temperature, relative humidity, and wind-velocity were obtained from sea-level up to the extreme height of 2200 meters, although wind-velocity was recorded to an altitude of 3100 meters. The direction of the wind was obtained by measuring the azimuth of the kites. Direct observations were made by Mr. Clayton upon the Peak of Teyde (Teneriffe) to a height of 3700 meters, and upon the Peak of Fogo (Cape Verdes) to 2200 meters, and observations of clouds enabled the wind to be ascertained about 500 meters higher. To attain a greater height in the free air than was possible with kites, the "Otaria" was provided with large paper balloons, eleven of which, filled with hydrogen gas, were liberated from the islands of St. Michaels (Azores), Madeira, 4 Conférence de la Commission Internationale pour l'Aérostation Scientifique, St. Pétersbourg, 1904, Supplément 7. Teneriffe (Canaries), and St. Vincent (Cape Verdes). Since these balloons were only intended to show the atmospheric drift, they did not carry self-recording instruments, and their direction and velocity at increasing heights were determined from angular measurements at the ends of a base-line laid off on the lee shore of the islands mentioned. One balloon, carrying a self-recording barometer and thermometer, was launched from the yacht off the island of Palma (Canaries), but, though its drift was observed, the balloon could not be recovered. It was found possible sometimes to follow the balloons in the telescope until they reached a height of 11,000 or 12,000 meters. The observations obtained with the kites at 500 and 1000 meters, and the simultaneous observations at sea-level, are given in Table I, which is divided into two parts, the first containing the observations made in an east-southeast direction across the Atlantic, and the second part those made in a southerly direction within the northeast trade and on its borders. West of the Azores, on the westerly slope of the permanent area of high barometric pressure, the observations between longitudes 69° and 39° show a slow decrease of temperature with increase of height, amounting to 4.5° per 1000 meters. In the lower 500 meters the decrease is only 0.24° per 100 meters, owing to inversions of temperature within the first few hundred meters in half the flights. In the next 500 meters there is the more rapid decrease of 0.66° per 100 meters. Upon the easterly and southeasterly slopes of the high pressure, between longitudes 25° and 19°, latitudes 38° and 33° north, the temperature falls at the adiabatic rate of one degree per 100 meters in the lower 500 meters, and then declines more slowly, namely, 0.20° per 100 meters, up to 1000 meters. The adiabatic rate appears to prevail over the ocean at night as well as in the daytime, and the bases of the cumulus clouds generally are not higher than 500 meters. The relative humidity decreases with height on the west of the high pressure, and increases to above 500 meters on the southeast side. In the former region southwest winds prevail, and in the latter locality northeast winds, the southwest winds turning to the left when facing them up to 500 meters, with increasing velocity up to 1000 meters, and the northeast winds turning to the right and increasing slightly in velocity up to 500 meters, but diminishing above that level. The mean directions and velocities in this table are resultants derived geometrically. In the column for wind-direction, a plus sign before the figures representing the differences per hundred meters indicates a turning towards the right hand, and a minus sign a turning towards the left. The observations on the northern edge of the northeast trade, that is, |