The Use of Kites for Meteorological Observations in the Upper Air

Abstract

ATTEMPTS to use kites for meteorological observations in the upper air began more than a century ago. The lack of light instruments which record automatically and continuously, prevented the success of the early experimenters. Such records are now obtained for the first time by means of kites at the Blue Hill Meteorological Observatory, near Boston. A history of kite-flying for meteorological observations, with a general account of the work at the Blue Hill Observatory, was given by the Director, Mr. Rotch, in a paper read before the Physical Section of the British Association at the Liverpool meeting (1896). Notes in NATURE of October 22 and 29, vol. liv. pp. 598 and 629, mention briefly the altitudes to which a meteorograph has been lifted at Blue Hill during the past summer. A few of the details of the recent highest ascent may be of interest to the readers of NATURE, especially as it shows that clear and definite meteorological records can be obtained at a great height by means of kites, at a comparatively small expense. The meteorograph weighs three pounds, and records temperature, humidity, and atmospheric pressure. The record of October 8, from the earth's surface to an altitude of 9375 feet above sea level, was as clear and sharp as the records of similar instruments in thermometer screens at the observatory. The temperature scale on the chart is centigrade, and the humidity pen records 10 per cent, too low, so that 90 per cent, represents saturation. The barograph-pen is made to record altitudes in metre; but it went entirely off the scale, which is too small for the altitude reached. The record was, however, completed on the part of the chart above the scale. A determination of the altitude was made by placing the barograph under an air-pump, and finding the fall of pressure necessary to raise the barograph-pen to the highest point recorded when on the kite. From the amount of fall and the temperature recorded by the thermographs on the kite and at the observatory, the altitude was computed. The altitude was also computed from the angular elevation of the kites and the length of line recorded by a reel, 3 per cent, being allowed for the sag of the steel wire holding the kites. The amount of the sag was determined by previous the odolite measurement, from a long base line, of the altitude of the kites. The altitudes by the two methods agreed within 1 per cent, of the height, and the mean of the two is given. In this ascent nine kites with a total area of about 170 square feet and 18,000 feet of steel wire, weighing about 46 lbs., were used. All the work of the ascent was managed with an ordinary wooden windlass by the three members of the staff—Mr. Fergusson, Mr. Sweetland and myself. The sea-coast is about six miles from Blue Hill, and the general level of the surrounding land is about 100 feet above sea-level. The top of Blue Hill, from which the kites were flown, is 635 feet above sea-level. Cumulus clouds had begun to form when the ascent began, and the meteorograph was soon elevated to the cloud-level, as shown by the humidity record, and was then lowered to remove a defective kite. In the second ascent the clouds were entered at an altitude of 4500 feet. The successive kites added to lift the line as they rose to the cloud-level, and again, when they were drawn below it, gave the data for numerous successive determinations of the altitude of the bases of the cumulus clouds, and furnish an example of the accuracy and frequency with which clouds can be measured in this manner, as shown by the following results:—