One of the objects sought was the collection of samples of air at great heights, but this was not accomplished until recently. In the first apparatus for this purpose, an aneroid barometer at a predetermined pressure turned the cock communicating with an exhausted receiver that filled with air and was then closed. The cock leaked, so next the ingenious device of generating heat chemically to seal the glass tube was tried. This, too, failed, but finally, an apparatus of M. Cailletet solved the problem. It is advisable to control the height deduced from the barometric records by direct observations so long as the balloon remains visible, and for this purpose micrometric measures were made with a telescope as soon as the balloon left the ground. There was also used a species of registering theodolite which, when kept pointed at the balloon, automatically traced on paper its azimuth and angular altitude. These records, when combined with the barometric height at a known hour, permitted the horizontal distance traversed, and hence the velocity, to be calculated, or, with two such instruments at ends of a base line, the height of the balloon could be found. The first experiments with _ballons-sondes_ in France were soon repeated in Germany, where a balloon of rubber-fabric holding 8700 cubic feet was obtained by the German Society for the Promotion of AÎrial Navigation. When inflated with coal-gas it had a lifting force of about two hundred and ninety pounds, in excess of its envelope, etc., weighing ninety-three pounds, and the meteorological apparatus weighing six pounds. The _Cirrus_, as it was called, burst on its first trial, but in July 1894 it made a remarkable voyage from Berlin to the boundary of Bosnia, a distance of seven hundred miles, at an average speed of sixty-two miles an hour. A maximum height of 54,000 feet and a minimum temperature of -63∞ Fahrenheit were recorded. The _Cirrus_ on its third voyage was accompanied by manned balloons in order to have simultaneous observations at different levels, and this time it travelled eighty-three miles an hour and rose 61,000 feet. The lowest temperature of -88∞ Fahrenheit was supposed to be too high, for the reason that whereas the ventilation of the thermometers in a rapidly ascending or descending balloon might be sufficient to counteract solar radiation, this would not be the case when the balloon was approaching its culminating point with a diminishing speed. Therefore, Dr. Assmann, under whose supervision the German experiments were conducted, employed the thermometer, which in the captive balloon was aspirated electrically, but now was driven by a weight, and later, because the ink froze, the registration was made photographic. The efficacy of the aspirator was seen in the ascent referred to, for, when its action stopped, a higher temperature was recorded though the balloon continued to ascend. In April 1895 the _Cirrus_ rose to the extraordinary height of 72,000 feet, or more than