The Dominion of the Air [47]
fulfilling one out of many engagements, found himself in a dilemma which bore resemblance in a slight degree to a far more serious predicament in which the writer became involved, and which must be told in due place. The preparations for the ascent, which was from the Mile End Road, had been hurried, and after finally getting away at a late hour in the evening, it was found that the valve line had got caught in a fold of the silk, and could not be operated. In consequence, the balloon was, of necessity, left to take its own chance through the night, and, after rising to a considerable height, it slowly lost buoyancy during the chilly hours, and, gradually settling, came to earth near Basingstoke, where the voyager, failing to get help or shelter, made his bed within his own car, lying in an open field, as other aeronauts have had to do in like circumstances.
Coxwell tells of a striking phenomenon seen during that voyage. "A splendid meteor was below the car, and apparently about 600 feet distant. It was blue and yellow, moving rapidly in a N.E. direction, and became extinguished without noise or sparks."
CHAPTER XI. THE BALLOON IN THE SERVICE OF SCIENCE.
At this point we must, for a brief while, drop the history of the famous aeronaut whose early career we have been briefly sketching in the last chapter, and turn our attention to a new feature of English ballooning. We have, at last, to record some genuinely scientific ascents, which our country now, all too tardily, instituted. It was the British Association that took the initiative, and the two men they chose for their purpose were both exceptionally qualified for the task they had in hand. The practical balloonist was none other than the veteran Charles Green, now in his sixty-seventh year, but destined yet to enjoy nearly twenty years more of life. The scientific expert was Mr. John Welsh, well fitted for the projected work by long training at Kew Observatory. The balloon which they used is itself worthy of mention, being the great Nassau Balloon of olden fame.
Welsh was quick to realise more clearly than any former experimentalist that on account of the absence of breeze in a free balloon, as also on account of great solar radiation, the indications of thermometers would, without special precautions, be falsified. He therefore invented a form of aspirating thermometer, the earliest to be met with, and far in advance of any that were subsequently used by other scientists. It consisted of a polished tube, in which thermometers were enclosed, and through which a stream of air was forced by bellows.
The difficulty of obtaining really accurate readings where thermometers are being quickly transported through varying temperatures is generally not duly appreciated. In the case of instruments carried m a balloon it should be remembered that the balloon itself conveys, clinging about it, no inconsiderable quantity of air, brought from other levels, while the temperature of its own mass will be liable to affect any thermometer in close neighbourhood. Moreover, any ordinary form of thermometer is necessarily sluggish in action, as may be readily noticed. If, for example, one be carried from a warm room to a cold passage, or vice versa it will be seen that the column moves very deliberately, and quite a long interval will elapse before it reaches its final position, the cause being that the entire instrument, with any stand or mounting that it may have, will have to adapt itself to the change of temperature before a true record will be obtained. This difficulty applies unavoidably to all thermometers in some degree, and the skill of instrument makers has been taxed to reduce the errors to a minimum. It is necessary, in any case, that a constant stream of surrounding air should play upon the instrument, and though this is most readily effected when instruments are carried aloft by kites, yet even thus it is thought that an interval of some minutes has to elapse before any form of thermometer will faithfully record any definite change of temperature.
Coxwell tells of a striking phenomenon seen during that voyage. "A splendid meteor was below the car, and apparently about 600 feet distant. It was blue and yellow, moving rapidly in a N.E. direction, and became extinguished without noise or sparks."
CHAPTER XI. THE BALLOON IN THE SERVICE OF SCIENCE.
At this point we must, for a brief while, drop the history of the famous aeronaut whose early career we have been briefly sketching in the last chapter, and turn our attention to a new feature of English ballooning. We have, at last, to record some genuinely scientific ascents, which our country now, all too tardily, instituted. It was the British Association that took the initiative, and the two men they chose for their purpose were both exceptionally qualified for the task they had in hand. The practical balloonist was none other than the veteran Charles Green, now in his sixty-seventh year, but destined yet to enjoy nearly twenty years more of life. The scientific expert was Mr. John Welsh, well fitted for the projected work by long training at Kew Observatory. The balloon which they used is itself worthy of mention, being the great Nassau Balloon of olden fame.
Welsh was quick to realise more clearly than any former experimentalist that on account of the absence of breeze in a free balloon, as also on account of great solar radiation, the indications of thermometers would, without special precautions, be falsified. He therefore invented a form of aspirating thermometer, the earliest to be met with, and far in advance of any that were subsequently used by other scientists. It consisted of a polished tube, in which thermometers were enclosed, and through which a stream of air was forced by bellows.
The difficulty of obtaining really accurate readings where thermometers are being quickly transported through varying temperatures is generally not duly appreciated. In the case of instruments carried m a balloon it should be remembered that the balloon itself conveys, clinging about it, no inconsiderable quantity of air, brought from other levels, while the temperature of its own mass will be liable to affect any thermometer in close neighbourhood. Moreover, any ordinary form of thermometer is necessarily sluggish in action, as may be readily noticed. If, for example, one be carried from a warm room to a cold passage, or vice versa it will be seen that the column moves very deliberately, and quite a long interval will elapse before it reaches its final position, the cause being that the entire instrument, with any stand or mounting that it may have, will have to adapt itself to the change of temperature before a true record will be obtained. This difficulty applies unavoidably to all thermometers in some degree, and the skill of instrument makers has been taxed to reduce the errors to a minimum. It is necessary, in any case, that a constant stream of surrounding air should play upon the instrument, and though this is most readily effected when instruments are carried aloft by kites, yet even thus it is thought that an interval of some minutes has to elapse before any form of thermometer will faithfully record any definite change of temperature.