weight of the air as the height increased. All that was then known upon this and the other points just mentioned depended upon observations made upon mountain-sides; and these were obviously vitiated by local influences, by terrestrial attractions exerted upon the superposed air, and by the presence of organic bodies, vegetable or animal. To catch the high air in its native purity, it must be soared into, and the balloon was the tool for the work.

The Coxwell of that period was one named Robertson, a native of Liége, a versatile genius; first a divine, then a professor of physics, then a phantasmagoriast, lastly an aëronaut. He built a small balloon thirty feet diameter, and generated hydrogen enough to fill it by decomposing water; he furnished the car for scientific observations with barometer, thermometer, timepiece, telescopes, birds, pigeons, phials to catch air in, and all necessaries and accessories. The Academy found the money, and appointed one of its members, M. Sacharoff, a chemist, to make the ascent with M. Robertson. It was on the 30th of June 1804 that this the first of scientific aërial voyages was made; the start was from the Jardin des Cadets in St. Petersburg, at seven o'clock in the evening. We need not follow the log of the journey; of late we have had relations of this sort almost ad nauseam. Suffice it to say, that the observers read their barometer and thermometer now and then, not apparently with much system, threw their pigeons, bottled the air at various heights up to about five thousand feet-their maximum altitude-ate their supper, determined to make the night of it, and joined hands to bind their intention, but afterwards thought better of it and came down, after a run of sixty versts that occupied about three hours. Two facts were noted that deserve separate mention. One was, that the needle of a compass inclined itself from the horizontal about ten degrees. An inclining or dipping' needle, as it is called, was taken up, but it was deranged, so that this singular vagary, important to magnetic science, could not be fairly examined. The other fact was, that when the aëronauts shouted through a speaking-trumpet, the sonorous percussions of the air produced a slight undulation of the balloon. Here was shadowed the power of man to rend the air by artificial thunders, to brew storms by repeated discharges of heavy cannon or any other great noises.

Science did not gain much from this ascent, directly; but the ball was set a-rolling, and very soon it was taken up by more illustrious players. In less than two months Biot and Gay-Lussac were up in a balloon. Their intentions bore chiefly on magnetic observations. Robertson, in the above voyage and in an earlier one, had suspected that the magnetic force which directs the compass-needle upon the earth's surface becomes enfeebled when the needle is carried high into the air. Saussure thought the same thing from his mountain experience. It was an important point to prove, because

much of the theory of terrestrial magnetism depended upon it. To determine the relative intensity of the earth's magnetic power in different situations, a delicately suspended needle is set in vibration; the greater the terrestrial force, the sooner will it be pulled from its diverted to its normal position, and so the quicker will be its period of oscillation; conversely, the less the force, the slower will it be pulled back, and the more protracted the vibrations. The magnet is like a straying youth-the more attractive the influence over him, the sooner is he brought to steadiness.

Biot and Gay-Lussac, equipped with the necessary magnets and chronometers to count the times of vibration, started from the garden of the Conservatoire des Arts et Métiers on the 24th of August 1804. Their balloon was but small, and would only lift them about four thousand yards; and when they tried to make the desired observations upon the swinging needle, they were all but entirely frustrated, because of the rotatory motion of the balloon. They counted a few oscillations, and very soon came down; I have heard it said, because one or both got frightened, but I find no documentary evidence on the point. One thing, however, is certain: when the next ascent was made, Gay-Lussac went up alone. This was on the 16th of September in the same year. He reached an altitude of nearly eight thousand yards, by throwing all useless appurtenances overboard; among other things he cast away a roughly-made chair, which fell in a thicket near to a yokel who was guarding some sheep. The sky was clear; but the balloon, nearly four miles high, was invisible. Imagine the astonishment of the natives! It was voted that the seat had come from heaven; but the knowing ones rejected this hypothesis on the grounds of the bad work that the article exhibited. The celestial chair-makers, said they, could not be such slovenly carpenters. The matter was under dispute till the newspapers told of the aëronaut's doings; and then the mystery vanished, no doubt much to the disappointment of the wondermongers.

The magnetic observations were a little more successful this time, but the results were not of a very decisive character: there were slight differences in the periods of vibration of the needle at different heights, but they did not follow a regular law of diminution; and on the whole it was concluded that the differences were accidental, and that the earth's magnetic force was the same at all altitudes above the surface. Such was the conclusion at the epoch of the observations; but since that time it has been discovered that temperature exerts a powerful influence over the rate of a needle's oscillations, cold quickening and warmth retarding them. If allowance be made for such an effect upon Gay-Lussac's needle, it results that his upper vibrations, made in a temperature of 16°, were relatively slower than his lower ones, which were made with the ther

mometer at 87°; and hence that the earth's magnetic force does diminish as we go upwards.

Besides these, the staple of his observations, Gay-Lussac recorded the indications of meteorological instruments, and deduced that the temperature, which, as is well known, decreases with elevation, varies less near the earth than in regions at a medium height, and that the humidity diminishes with extreme rapidity. The actual decrease of temperature which he observed was 7210 of the Fahrenheit scale in ascending 22,896 feet, or about a degree in 316 feet; a decrement very similar to that deduced from the best of mountain-observations. He collected air at his upper limit and analysed it, and found that while it contained the same proportions of oxygen and nitrogen as near the earth, it offered no trace of hydrogen; a fact of some importance in refuting certain theories of fiery

meteors.

These French achievements made Italy jealous of her meteorological honours. The next scientific balloon ascent was made by a Neapolitan astronomer, one Carlo Brioschi, in company with the first of Italian aëronauts, Andreani. Their laudable ambition was to pass the limit attained by Gay-Lussac; so they went up and up, higher and higher, till they got into a highly rarefied region of the atmosphere, when their lofty intentions were unhappily frustrated; the balloon had a greater pressure inside than out, from the expansion of the gas, and it burst, bringing them down with a run. Fortunately the torn and empty bag acted the part of a parachute and checked the velocity of their descent, or they must have been dashed to pieces, as Cocking was years after. As it was, falling as they did, slowly and upon soft ground, they came off with their lives; but Brioschi received injuries that eventually caused his death.

Whether this unfortunate experiment scared the philosophers off their quest for knowledge, or whether they were deterred from the research by another fear to be presently alluded to, I know not; but it is certain that for forty years nothing was done for science by the balloon in any systematic manner; nothing beyond the isolated facts gleaned now and then by the more philosophical of professional aëronauts. About 1841, however, the subject was noised again, this time in England. The British Association, ever ready to find the needful for experiments too costly for individual undertaking, was induced to vote a sum of 2501. for instruments and balloons to make a regular series of aërial investigations. Some of the money was spent, and once a balloon was reported ready to ascend, but for some unrecorded reason it never went off. I hope personal vanities and jealousies were not the disturbing cause; more than one squabble having arisen out of disputed honours in the matter of scientific skying, the thought will intrude itself.

Eight or nine years more passed before another aërial ship was

launched in the cause of science, and then two plucky Frenchmen, MM. Bixio and Barral, entered themselves in this race for bubble fame. They were for resolving a multitude of questions: the laws of decrease of temperature and of humidity, the composition of the atmosphere, the comparative calorific effects of the solar rays at high elevations, the polarisation or non-polarisation of light from the clouds, and a number of minor matters. Everything promised well : Regnault furnished the instruments, Dupuis-Delcourt the balloon; seven or eight miles was the height of their ambition. But when the day of ascent came-it was the 29th of June 1850-matters looked gloomy: the rain fell in torrents; the balloon was torn by high winds, and had to be hurriedly patched-up. But the observers were intrepid, and rejecting proposals for the abandonment of the ascent, they cast off, and in a minute were lost in the clouds. Once aloft the balloon dilated, pressed hard against the netting, and expanded downwards, covering the aëronauts. One of them, in trying to get at the valve-cord, made an opening in the neck and out rushed the gas, sickening and nearly suffocating them. Then they found they were descending rapidly, in consequence of a great slit that had formed in the equator of the bag. Destruction seemed imminent; there was no hope but by casting away every weighty article in the car. This they did, sacrificing all but their precious instruments, and with happy effect, for they came down without serious hurt, a soft vineyard receiving them.

One would think that such an adventure would have checked, if it did not destroy, the ardour of the observers. But no; before a month had elapsed, they were up again, in the same balloon, and in the midst of a rain-storm and a turbulent atmosphere. It was in some respects fortunate that they ascended; for they saw and felt what a serene sky would not have manifested to them. The cloud into which they plunged turned out to be about three miles thick, and when they were nearly through it they beheld a curious phenomenon. The sun was shining above them, and below the level of the car there appeared another sun, reflected from what looked like a stratum of water lying there beneath. It was not really water, however, but a film of minute crystals of ice floating in the vaporous cloud. The aëronauts were at one time completely covered with these frozen spicule. But the extraordinary thing was the enormous cold experienced in the cloud. Gay-Lussac, at the height of 7000 metres, found the temperature 9 degrees centigrade below zero; MM. Bixio and Barral registered 30 degrees lower than this. There was no doubt of the fact; it was no error of observation, for all the instruments confirmed it; and, as Arago said, it was a discovery of the highest interest to meteorology. While it gives us a glimpse into the foundry where hailstones are formed, it puzzles us sorely to account for their formation; for what can be the constitu

tion of a cloud that parts with its heat so entirely, and admits of such a prodigious refrigeration?

This ascent gave abnormal results: it could not do otherwise, since it was made under such abnormal circumstances. The information specially sought was not procured; and I do not find that MM. Bixio and Barral, although they had all the instrumental equipment, ever ascended again.

The observers

Strange does it appear that all the aërial researches were abandoned almost at their birth. Robertson, Gay-Lussac, Bixio, all, as it were, strangled their offspring. Why was this? One reason, known to apply in one case, perhaps applies to all. came to be regarded in the public eye in the same light as the balloonists who went up for lucre, and the acrobats who hung by their feet over cars to amuse gaping crowds at a shilling a head. As they did not like the association, they abandoned the pursuit. In more recent times, we have seen longer series of observations repeated in systematic manner. Have the public altered their views? or have the balloon-observers of to-day overcome the scruples that troubled their predecessors ?

The first systematic series of ascents was made in the year 1852, by Mr. Welsh, then director of the British Association Observatory at Kew. They were four in number, and their dates were, August 17th and 26th, October 21st, and November 10th. Green's Nassau balloon was the ascending medium, and Vauxhall Gardens was the starting-place. The results that were obtained were the most valuable of any up to their date. Mr. Welsh was a good observer, and read his instruments with great regularity, at very short intervals. When his observations were fully discussed, they proved that the downward march of temperature is not uniform, but that at a certain height, which varies with the season, the regular diminution is arrested, and for the space of about 2000 feet the temperature remains constant, or even increases slightly; afterwards resuming its downward course. This interruption was found to coincide with a great fall in the temperature at which dew is formed the dew-point, as it is termed. Making allowance for this irregularity, it was determined that the fall of temperature was about one degree in 296 feet, as an average from all the observationssensibly the same as that obtained by Gay-Lussac. Air was bottled during the ascents, and afterwards analysed, and found to differ in no important degree from that collected near the earth at the same time. Welsh made no magnetic observations.

For seven or eight years the meteorologists felt no thirst for the knowledge which the balloon might give them, notwithstanding the high importance they had at various times attached to it; but when a new fit came over them, it was a powerful one, and aërial thermometer-reading made more noise than ever. A committee of the