Читать книгу Falling Upwards: How We Took to the Air - Richard Holmes - Страница 13

In 1785 Tiberius Cavallo, a Fellow of the Royal Society, put together the first British study of ballooning. His A Treatise on the History and Practice of Aerostation studiously adopted the French scientific term for ‘lighter-than-air’ flight, but moved far beyond national rivalries. He wanted to consider the phenomenon of flight from both a scientific and a philosophical point of view. He thought that ballooning held out immense possibilities, less as a transport device than as an instrument for studying the upper air and the nature of weather. This distinction between horizontal and vertical travel would have a long subsequent history.

Cavallo was a brilliant Italian physicist who had moved to London at the age of twenty-two, and had already written extensively on magnetism and electrical phenomena. Elected to the Royal Society in 1779, he quickly turned his attention to ballooning. He had some claims to be one of the first to inflate soap bubbles with hydrogen as early as 1782. Although a handsome portrait is held by the National Portrait Gallery in London, he is now largely and unjustly forgotten. Yet his study emerges as the most authoritative early treatise on the subject of ballooning in either English or French. The copy of Cavallo’s book held by the British Library is personally inscribed ‘To Sir Joseph Banks from the Author’, in severe black ink.

Cavallo carefully adopted a considered and even sceptical tone, well calculated to appeal to Banks. Much had been made of Vincenzo Lunardi’s historic first flight in Britain, in September 1784, when he flew from London to Hertfordshire with his pet cat. The newspapers of the day all declared Lunardi a heroic pioneer, a patriot and an animal lover, although the gothic novelist Horace Walpole – author of The Castle of Otranto – roundly criticised him for risking the life of the said cat. But Cavallo noted: ‘Besides the Romantic observations which might be naturally suggested by the Prospect seen from that elevated situation, and by the agreeable calm he felt after the fatigue, the anxiety, and the accomplishment of his Experiment, Mr Lunardi seems to have made no particular philosophical observation, or such as may either tend to improve the subject of aerostation, or to throw light on any operation in Nature.’^{23 fn7}

Cavallo analysed and dismissed most claims to navigate balloons, except by the use of different air currents at different altitudes.²⁴ He emphasised the aeronaut’s vulnerability to unpredictable atmospheric phenomena such as down-drafts, lightning strikes and ice formation. He deliberately included the first alarming account of a French balloon caught in a thunderstorm, during an ascent from Saint-Cloud in July 1784, and dragged helplessly upwards by a thermal:

Three minutes after ascending, the balloon was lost in the clouds, and the aerial voyagers lost sight of the earth, being involved in dense vapour. Here an unusual agitation of the air, somewhat like a whirlwind, in a moment turned the machine three times from the right to the left. The violent shocks, which they suffered prevented their using any of the means proposed for the direction of the balloon, and they even tore away the silk stuff of which the helm was made. Never, said they, a more dreadful scene presented itself to any eye, than that in which they were involved. An unbounded ocean of shapeless clouds rolled one upon another beneath, and seemed to forbid their return to earth, which was still invisible. The agitation of the balloon became greater every moment … ²⁵

Yet for all this, Cavallo was a passionate balloon enthusiast. He recorded and analysed all the significant flights, both French and English, made from Montgolfier’s first balloon at Annonay in June 1783, to Blanchard and Jeffries’s crossing of the Channel in January 1785. He distinguished carefully between hot-air and hydrogen balloons, and their quite different flight characteristics. He looked in detail at methods of preparing hydrogen gas, noting that Joseph Priestley had come up with one that used steam rather than sulphuric acid. He also examined the different ways of constructing balloon canopies from rubber (‘cauchou’), waxed silk, varnished linen and taffeta.

In a longer perspective, he stressed the astonishing speed of aerial travel over the ground – ‘often between 40 and 50 miles per hour’ – combined with its incredible ‘stillness and tranquillity’ in most normal conditions.²⁶ This he thought must eventually revolutionise our fundamental ideas of transport and communications, even if the moment had not yet arrived. But he was less impressed by the horizontal potential of ballooning than by its vertical one. The essence of flight lay in attaining an utterly new dimension: altitude.

He pointed out that in achieving altitudes of over two miles, balloons opened a whole new perspective on mankind’s observations of the earth beneath. Man’s growing impact on the surface of the planet for the first time became visible. As did the vast tracts of the earth – mountains, forests, deserts – yet to be traversed or discovered. Above all he stressed that the full potential of flight had not yet been remotely explored. The situation has perhaps some analogies with the space exploration programme, in the years following the Apollo missions.

Cavallo considered the whole range of possible balloon applications. But he finally and presciently championed its relevance to the infant science of meteorology:

The philosophical uses to which these machines may be subservient are numerous indeed; and it may be sufficient to say, that hardly anything of what passes in the atmosphere is known with precision, and that principally for want of a method of ascending into the atmosphere. The formation of rain, of thunderstorms, of vapours, hail, snow and meteors in general, require to be attentively examined and ascertained.

The action of the barometer, the refraction and temperature of air in various regions, the descent of bodies, the propagation of sound etc are subjects which all require a long series of observations and experiments, the performance of which could never have been properly expected, before the discovery of these machines. We may therefore conclude with a wish that the learned, and the encouragers of useful knowledge, may unanimously concur in endeavouring to promote the subject of aerostation, and to render it useful as possible to mankind. ²⁷

Cavallo’s work was both a challenge and an intellectual landmark in the early history of ballooning. He was largely responsible for the historic first article on ‘Aerostation’, which appeared in the Encyclopaedia Britannica, with notable illustrations, in 1797. This was a signal date. From then on, flight was officially established as a new branch of scientific knowledge, rather than an old backwater of mythology.