Although Mr. Eddy began flying kites as a diversion, he soon saw that there were more serious reasons for continuing his experiments. Having long been interested in meteorological problems, it occurred to him that good results might be obtained by sending aloft, on kite-strings, self-registering thermometers and apparatus for indicating the direction and strength of the air currents. On February 4, 1891, he sent up what is believed to be the first thermometer ever attached to a kite for scientific purposes. This was at nine o'clock in the evening on a cold winter's night, the thermometer registering ten degrees Fahrenheit at the ground. On reading the record after the descent, the thermometer was found to mark six degrees Fahrenheit, which indicated, according to the recognized law of decrease of temperature, that the kite had been sent to a height of one thousand feet. The law is that in ascending from the earth the temperature falls one degree for every two hundred and fifty feet; but subsequent experiments convinced Mr. Eddy that it was by no means to be relied upon as an indication of the height of kites. Not that the law is false; but it holds good only when the meteorological conditions above are the same as at the earth's surface, which is very far from being the case always. Out of these experiments Mr. Eddy evolved an important theory which has since been abundantly verified. Seeing the frequent variations in the thermometric readings from what the law had led him to expect, he concluded that these were due to meteorological variations overhead; and that changes in the weather, say the approach of warm waves or cold waves, make themselves felt in the air strata above the earth's surface several hours before they can be detected at the surface. Observations extending over months at the Blue Hills Observatory, near Boston, and elsewhere, have abundantly confirmed this theory. With this fact established, it followed, in Mr. Eddy's opinion, that it was perfectly possible to use kites in making weather prognostications; and, indeed, he has been doing this himself for several years with the best results. Whenever his kite-thermometers, sent to a fixed height which he determines independently by a specially devised kite-quadrant, show actual readings which are either warmer or cooler than the theoretical readings, he prophesies that the weather will, within a few hours, become warmer or colder at the earth's surface, and these prophecies are fulfilled in a large majority of cases. If the kite-thermometers show exactly the temperature which the law would call for, he prophesies that there will be no change in the weather. [Illustration: CITY HALL PARK AND BROADWAY FROM A KITE. From a photograph taken from a kite by Mr. W.A. Eddy. City Hall Park, New York City, appears in the foreground, with Broadway back of it.]