In the spring of 1875, and with the co-operation of French scientific societies, it was determined to make two experimental voyages in a balloon called the "Zenith," one of these to be of long duration, the other of great height. The first of these had been successfully accomplished in a flight of twenty-four hours' duration from Paris to Bordeaux. It was now April the 15th, and the lofty flight was embarked upon by M. Gaston Tissandier, accompanied by MM. Croce-Spinelli and Sivel. Under competent advice, provision for respiration on emergency was provided in three small balloons, filled with a mixture of air and oxygen, and fitted with indiarubber hose pipes, which would allow the mixture, when inhaled, to pass first through a wash bottle containing aromatic fluid. The experiments determined on included an analysis of the proportion of carbonic acid gas at different heights by means of special apparatus; spectroscopic observations, and the readings registered by certain barometers and thermometers. A novel and valuable experiment, also arranged, was that of testing the internal temperature of the balloon as compared with that of the external air. Ascending at 11.30 a.m. under a warm sun, the balloon had by 1 p.m. reached an altitude of 16,000 feet, when the external air was at freezing point, the gas high in the balloon being 72 degrees, and at the centre 66 degrees. Ere this height had been fully reached, however, the voyagers had begun to breathe oxygen. At 11.57, an hour previously, Spinelli had written in his notebook, "Slight pain in the ears--somewhat oppressed--it is the gas." At 23,000 feet Sivel wrote in his notebook, "I am inhaling oxygen--the effect is excellent," after which he proceeded to urge the balloon higher by a discharge of ballast. The rest of the terrible narrative has now to be taken from the notes of M. Tissandier, and as these constitute one of the most thrilling narratives in aeronautical records we transcribe them nearly in full, as given by Mr. Glaisher:--