Now that the possibility of lifting self-recording meteorological instruments to considerable heights had been demonstrated, an investigation of the thermal and hygrometric conditions of the free air was undertaken by the staff of the Blue Hill Observatory, who had already made an investigation of the movements of the clouds by the methods described in the second chapter. The development of the kite and its accessory apparatus, and the acquisition of the knowledge how to use them, required much time, and resulted in the damage or loss of many kites. Two meteorographs, as the combination of two or more self-recording instruments is called, were dropped from a great height and no trace of them was found. When, however, by the breaking of the line both kites and instrument are carried away, the kites act as a parachute and bear the instrument gently to the ground, where both are usually recovered uninjured; to facilitate their return should they fall at a distance, the name and address are marked on each. It would be tedious to relate the ups and downs of scientific kite-flying at Blue Hill before the wind was successfully harnessed to the service of science, and the kites were prevented from kicking over the traces, or from breaking away, so only a brief account of the progress of the work will be given, and then the methods at present used will be described. At first the Eddy, or Malay kites, as they are also called, covered with paper or with varnished cloth, were coupled tandem to secure greater safety and lifting power. The principle of attaching kites at several points on the line was early adopted at Blue Hill, for although it can be demonstrated theoretically that a greater height is possible by concentrating all the pull at the end of the line, yet in the case of a line which is not infinitely strong the best results are got by distributing the pull, and in this way, too, kites can be added as the wind conditions aloft warrant. To obviate the frequent breaking of the bowed cross-piece, Mr. Fergusson made it in two pieces, each being held in a metal socket on the central stick, the two pieces forming a dihedral angle towards the wind. It had the advantage also of being readily taken apart for transportation. This kite, shown in Fig. 8, flew at a high angle above the horizon and through a considerable range of wind velocity, but it could not be kept permanently in balance, or made to adjust itself to great variations in wind velocity, and therefore it was discarded.