traces of the latter it was computed that at an altitude of about 49,000 feet a temperature of -60∞ Fahrenheit had been met with, both pressure and temperature being the lowest measured in a balloon up to that time. Although the data secured by this ascent were somewhat doubtful, yet the feasibility of exploring the atmosphere by _ballons-sondes_ was proved. It was seen that the enormous velocity of ascent overcame the wind and permitted the path of the balloon to the summit of its trajectory to be followed, the balloon appearing like a meteor visible in daylight, and so its height could be calculated by trigonometrical measurements; while the descent, caused by the escape and cooling of the gas, was gentle and regular, permitting the delicate instruments to be recovered uninjured. [Illustration: FIG. 5.--Baro-thermograph of Richard.] [Illustration: FIG. 6.--The _AÈrophile_ rising. The left-hand picture shows the deformation caused by the resistance of the air to its rapid ascent, and the right-hand one the violent oscillations when first liberated.] The second ascent of this _AÈrophile_ was its last, for, after falling in the Black Forest, it was burned by children. However, M. BesanÁon, not discouraged, constructed the _AÈrophile II._ of 6300 cubic feet, and improved the instruments as experience suggested. The records had often been interrupted by freezing of the ink, so the pen was replaced by a needle marking with less friction on smoked paper surrounding the record drum. To avoid heating of the thermometers by the sun, they were placed in a wicker cylinder open at both ends and covered with bright metallic paper. This was hung below the balloon with its axis vertical, in order that the draught through the cylinder when the balloon was rising or falling should counteract the insolation, and in the next ascent, at about the same altitude, a temperature lower by 36∞ Fahrenheit indicated the effect of the protection. To secure an independent record of the lowest temperature an ingenious device was used, consisting of a thermometer tube filled with alcohol and having black divisions. The lowest point to which the alcohol sank was recorded on photographic paper placed behind the tube, the whole being enclosed in a metallic box that was automatically closed on striking the ground, and so was preserved against the meddling of curious persons. Up to the middle of 1898 ten voyages had been made by the _AÈrophiles_, which were now constructed of varnished silk to hold 16,000 cubic feet of gas.