Wise, by his expedient of tying ribbons at different points to his trail rope, would obtain much more correct and constant information respecting those general streams through which the pendant rope was moving. A similar expedient adopted by the same ingenious aeronaut is worthy of imitation, namely, that of tying ribbons on to a rod projecting laterally from the car. These form a handy and constant telltale as to the flight of the balloon, for should they be fluttering upwards the sky sailor at once knows that his craft is descending, and that he must act accordingly.
The material, pure silk, which was universally adopted up to and after the period we are now regarding, is not on every account to be reckoned the most desirable. In the first place, its cost alone is prohibitive, and next, although lighter than any kind of linen, strength for strength, it requires a greater weight of varnish, which, moreover, it does not take so kindly as does fabric made of vegetable tissue.
Further, paradoxical as it may appear, its great strength is not entirely an advantage. There are occasions which must come into the experience of every zealous aeronaut when his balloon has descended in a rough wind, and in awkward country. This may, indeed, happen even when the ascent has been made in calm. Squalls of wind may spring up at short notice, or after traversing only two or three counties a strong gale may be found on the earth, though such was absent in the starting ground. This is more particularly the case when the landing chances to be on high ground in the neighbourhood of the sea. In these circ.u.mstances, the careful balloonist, who will generally be forewarned by the ruffle on any water he may pa.s.s, or by the drift of smoke, the tossing of trees, or by their very rustling or "singing" wafted upwards to him, will, if possible, seek for his landing place the lee of a wood or some other sheltered spot. But, even with all his care, he will sometimes find himself, on reaching earth, being dragged violently across country on a mad course which the anchor cannot check. Now, the country through which he is making an unwilling steeplechase may be difficult, or even dangerous.
Rivers, railway cuttings, or other undesirable obstacles may lie ahead, or, worse yet, such a death trap as in such circ.u.mstances almost any part of Derbyshire affords, with its stone walls, its precipitous cliffs, and deep rocky dells. To be dragged at the speed of an express train through territory of this description will presently mean damage to something, perhaps to telegraph poles, to roofs, or crops, and if not, then to the balloon itself. Something appertaining to it must be victimised, and it is in all ways best that this should be the fabric of the balloon itself. If made of some form, or at least some proportion of linen, this will probably rend ere long, and, allowing the gas to escape, will soon bring itself to rest. On the other hand, if the balloon proper is a silk one, with sound net and in good condition, it is probable that something else will give way first, and that something may prove to be the hapless pa.s.senger or pa.s.sengers.
And here be it laid down as one first and all-important principle, that in any such awkward predicament as that just described, if there be more than one pa.s.senger aboard, let none attempt to get out. In the first place, he may very probably break a limb in so doing, inasmuch as the tangle of the ropes will not allow of his getting cut readily; or, when actually on the ground, he may be caught and impaled by the anchor charging and leaping behind. But, worse than all, he may, in any case, jeopardise the lives of his companions, who stand in need of all the available weight and help that the car contains up to the moment Of coming to final rest.
We have already touched on the early notions as to the means of steering a balloon. Oars had been tested without satisfactory result, and the conception of a rotary screw found favour among theorists at this time, the principle being actually tried with success in working models, which, by mechanical means, could be made to flit about in the still air of the lecture room; but the only feasible method advocated was that already alluded to, which depended on the undesirable action of a trail rope dragging over the ground or through water. The idea was, of course, perfectly practical, and was simply a.n.a.logous to the method adopted by sailors, who, when floating with the stream but without wind, are desirous of gaining "steerage way." While simply drifting with the flood, they are unable to guide their vessel in any way, and this, in practice, is commonly effected by simply propelling the vessel faster than the stream, in which case the rudder at once becomes available. But the same result is equally well obtained by slowing the vessel, and this is easily accomplished by a cable, with a small anchor or other weight attached, dragging below the vessel. This cable is essentially the same as the guide-rope of the older aeronauts.
It is when we come to consider the impressions and sensations described by sky voyagers of bygone times that we find them curiously at variance with our own. As an instance, we may state that the earth, as seen from a highflying balloon, used to be almost always described as appearing concave, or like a huge basin, and ingenious attempts were made to prove mathematically that this must be so. The laws of refraction are brought in to prove the fact; or, again, the case is stated thus: Supposing the extreme horizon to be seen when the balloon is little more than a mile high, the range of view on all sides will then be, roughly, some eighty miles. If, then, a line were drawn from the aerial observer to this remote distance, that line would be almost horizontal; so nearly so that he cannot persuade himself that his horizon is otherwise than still on a level with his eye; yet the earth below him lies, as it seems, at the bottom of a huge gulf. Thus the whole visible earth appears as a vast bowl or basin. This is extremely ingenious reasoning, and not to be disregarded; but the fact remains that in the experience of the writer and of many others whom he has consulted, there is no such optical illusion as I have just discussed, and to their vision it is impossible to regard the earth as anything but uniformly flat.
Another impression invariably insisted on by early balloonists is that the earth, on quitting it, appears to drop away into an abyss, leaving the voyagers motionless, and this illusion must, indeed, be probably universal. It is the same illusion as the apparent gliding backwards of objects to a traveller in a railway carriage; only in this latter case the rattling and shaking of the carriage helps the mind to grasp the real fact that the motion belongs to the train itself; whereas it is otherwise with a balloon, whose motion is so perfectly smooth as to be quite imperceptible.
Old ideas, formed upon insufficient observations, even if erroneous, were slow to die. Thus it used to be stated that an upper cloud floor adapted itself to the contour of the land over which it rested, giving what Mr. Monck Mason has called a "phrenological estimate" of the character of the earth below; the clouds, "even when under the influence of rapid motion, seeming to accommodate themselves to all variations of form in the surface of the subjacent soil, rising with its prominences and sinking with its depressions." Probably few aeronauts of the present time will accept the statement.
It used commonly to be a.s.serted, and is so often to this day, that a feeling as of sea-sickness is experienced in balloon travel, and the notion has undoubtedly arisen from the circ.u.mstances attending an ascent in a captive balloon. It were well, now that ballooning bids fair to become popular, to disabuse the public mind of such a wholly false idea.
The truth is that a balloon let up with a lengthy rope and held captive will, with a fitful breeze, pitch and sway in a manner which may induce all the unpleasant feelings attending a rough pa.s.sage at sea. It may do worse, and even be borne to earth with a puff of wind which may come unexpectedly, and considerably unsettle the nerves of any holiday pa.s.senger. I could tell of a "captive" that had been behaving itself creditably on a not very settled day suddenly swooping over a roadway and down into public gardens, where it lay incontinently along the ground, and then, before the astonished pa.s.sengers could attempt to alight, it was seized with another mood, and, mounting once again majestically skyward, submitted to be hauled down with all becoming grace and ease. It is owing to their vagaries and want of manageability that, as will be shown, "captives" are of uncertain use in war. On the other hand, a free balloon is exempt from such disadvantages, and at moderate heights not the smallest feeling of nausea is ever experienced.
The only unpleasant sensation, and that not of any gravity, ever complained of, is a peculiar tension in the ears experienced in a rapid ascent, or more often, perhaps, in a descent. The cause, which is trivial and easily removed, should be properly understood, and cannot be given in clearer language than that used by Professor Tyndall:--"Behind the tympanic membrane exists a cavity--the drum of the ear--in part crossed by a series of bones, and in part occupied by air. This cavity communicates with the mouth by means of a duct called the Eustachian tube. This tube is generally closed, the air s.p.a.ce behind the tympanic membrane being thus cut off from the external air. If, under these circ.u.mstances, the external air becomes denser, it will press the tympanic membrane inwards; if, on the other hand, the air on the other side becomes rarer, while the Eustachian tube becomes closed, the membrane will be pressed outwards. Pain is felt in both cases, and partial deafness is experienced.... By the act of swallowing the Eustachian tube is opened, and thus equilibrium is established between the external and internal pressure."
Founded on physical facts more or less correct in themselves, come a number of tales of olden days, which are at least more marvellous than credible, the following serving as an example. The scientific truth underlying the story is the well-known expedient of placing a shrivelled apple under the receiver of an air pump. As the air becomes rarefied the apple swells, smooths itself out, and presently becomes round and rosy as it was in the summer time. It is recorded that on one occasion a man of mature years made an ascent, accompanied by his son, and, after reaching some height, the youth remarked on how young his father was looking. They still continued to ascend, and the same remark was repeated more than once. And at last, having now reached attenuated regions, the son cried in astonishment, "Why, dad, you ought to be at school!" The cause of this remark was that in the rarefied air all the wrinkles had come out of the old man"s face, and his cheeks were as chubby as his son"s.
This discussion of old ideas should not be closed without mention of a plausible plea for the balloon made by Wise and others on the score of its value to health. Lofty ascents have proved a strain on even robust const.i.tutions--the heart may begin to suffer, or ills akin to mountain sickness may intervene before a height equal to that of our loftiest mountain is reached. But many have spoken of an exhilaration of spirits not inferior to that of the mountaineer, which is experienced, and without fatigue, in sky voyages reasonably indulged in--of a light-heartedness, a glow of health, a sharpened appet.i.te, and the keen enjoyment of mere existence. Nay, it has been seriously affirmed that "more good may be got by the invalid in an hour or two while two miles up on a fine summer"s day than is to be gained in an entire voyage from New York to Madeira by sea."
CHAPTER X. THE COMMENCEMENT OF A NEW ERA.
Resuming the roll of progressive aeronauts in England whose labours were devoted to the practical conquest of the air, and whose methods and mechanical achievements mark the road of advance by which the successes of to-day have been obtained, there stand out prominently two individuals, of whom one has already received mention in these pages.
The period of a single life is seldom sufficient to allow within its span the full development of any new departure in art or science, and it cannot, therefore, be wondered at if Charles Green, though reviving and re-modelling the art of ballooning in our own country, even after an exceptionally long and successful career, left that pursuit to which he had given new birth virtually still in its infancy.
The year following that in which Green conducted the famous Na.s.sau voyage we find him experimenting in the same balloon with his chosen friend and colleague, Edward Spencer, solicitor, of Barnsbury, who, only nine years later, compiles memoranda of thirty-four ascents, made under every variety of circ.u.mstance, many being of a highly enterprising nature. We find him writing enthusiastically of the raptures he experienced when sailing over London in night hours, of lofty ascents and extremely low temperatures, of speeding twenty-eight miles in twenty minutes, of grapnel ropes breaking, and of a cross-country race of four miles through woods and hedges. Such was Mr. Spencer the elder, and if further evidence were needed of his practical acquaintance with, as well as personal devotion to, his adopted profession of aeronautics, we have it in the store of working calculations and other minutiae of the craft, most carefully compiled in ma.n.u.script by his own hand; these memoranda being to this day constantly consulted by his grandsons, the present eminent aeronauts, Messrs. Spencer Brothers, as supplying a manual of reliable data for the execution of much of the most important parts of their work.
In the terrific ordeal and risk entailed by the daring and fatal parachute descent of c.o.c.king, Green required an a.s.sistant of exceptional nerve and reliability, and, as has been recorded, his choice at once fell on Edward Spencer. In this choice it has already been shown that he was well justified, and in the trying circ.u.mstances that ensued Green frankly owns that it was his competent companion who was the first to recover himself. A few years later, when a distinguished company, among whom were Albert Smith and Shirley Brooks, made a memorable ascent from Cremorne, Edward Spencer is one of the select party.
Some account of this voyage should be given, and it need not be said that no more graphic account is to be found than that given by the facile pen of Albert Smith himself. His personal narrative also forms an instructive contrast to another which he had occasion to give to the world shortly afterwards, and which shall be duly noticed. The enthusiastic writer first describes, with apparent pride, the company that ascended with him. Besides Mr. Shirley Brooks, there were Messrs.
Davidson, of the Garrick Club; Mr. John Lee, well known in theatrical circles; Mr. P. Thompson, of Guy"s Hospital, and others--ten in all, including Charles Green as skipper, and Edward Spencer, who, sitting in the rigging, was entrusted with the all-important management of the valve rope.
"The first sensation experienced," Albert Smith continues, "was not that we were rising, but that the balloon remained fixed, whilst all the world below was rapidly falling away; while the cheers with which they greeted our departure grew fainter, and the cheerers themselves began to look like the inmates of many sixpenny Noah"s Arks grouped upon a billiard table.... Our hats would have held millions.... And most strange is the roar of the city as it comes surging into the welkin as though the whole metropolis cheered you with one voice.... Yet none beyond the ordinary pa.s.sengers are to be seen. The noise is as inexplicable as the murmur in the air at hot summer noontide."
The significance of this last remark will be insisted on when the writer has to tell his own experiences aloft over London, as also a note to the effect that there were seen "large enclosed fields and gardens and pleasure grounds where none were supposed to exist by ordinary pa.s.sengers." Another interesting note, having reference to a once familiar feature on the river, now disappearing, related to the paddle boats of those days, the steamers making a very beautiful effect, "leaving two long wings of foam behind them similar to the train of a table rocket." Highly suggestive, too, of the experiences of railway travellers in the year 1847 is the account of the alighting, which, by the way, was obviously of no very rude nature. "Every time," says the writer, "the grapnel catches in the ground the balloon is pulled up suddenly with a shock that would soon send anybody from his seat, a jerk like that which occurs when fresh carriages are brought up to a railway train." But the concluding paragraph in this rosy narrative affords another and a very notable contrast to the story which that same writer had occasion to put on record before that same year had pa.s.sed.
"We counsel everybody to go up in a balloon... In spite of the apparent frightful fragility of cane and network nothing can in reality be more secure... The stories of pressure on the ears, intense cold, and the danger of coming down are all fictions.... Indeed, we almost wanted a few perils to give a little excitement to the trip, and have some notion, if possible, of going up the next time at midnight with fireworks in a thunderstorm, throwing away all the ballast, fastening down the valve, and seeing where the wind will send us."
The fireworks, the thunderstorm, and the throwing away of ballast, all came off on the 15th of the following October, when Albert Smith made his second ascent, this time from Vauxhall Gardens, under the guidance of Mr. Gypson, and accompanied by two fellow-pa.s.sengers. Fireworks, which were to be displayed when aloft, were suspended on a framework forty feet below the car. Lightning was also playing around as they cast off. The description which Albert Smith gives of London by night as seen from an estimated elevation of 4,000 feet, should be compared with other descriptions that will be given in these pages:--
"In the obscurity all traces of houses and enclosures are lost sight of. I can compare it to nothing else than floating over dark blue and boundless sea spangled with hundreds of thousands of stars. These stars were the lamps. We could see them stretching over the river at the bridges, edging its banks, forming squares and long parallel lines of light in the streets and solitary parks. Further and further apart until they were altogether lost in the suburbs. The effect was bewildering."
At 7,000 feet, one of the pa.s.sengers, sitting in the ring, remarked that the balloon was getting very tense, and the order was given to "ease her" by opening the top valve. The valve line was accordingly pulled, "and immediately afterwards we heard a noise similar to the escape of steam in a locomotive, and the lower part of the balloon collapsed rapidly, and appeared to fly up into the upper portion. At the same instant the balloon began to fall with appalling velocity, the immense ma.s.s of loose silk surging and rustling frightfully over our heads....
retreating up away from us more and more into the head of the balloon.
The suggestion was made to throw everything over that might lighten the balloon. I had two sandbags in my lap, which were cast away directly....
There were several large bags of ballast, and some bottles of wine, and these were instantly thrown away, but no effect was perceptible. The wind still appeared to be rushing up past us at a fearful rate, and, to add to the horror, we came among the still expiring discharge of the fireworks which floated in the air, so that little bits of exploded cases and touch-paper, still incandescent, attached themselves to the cordage of the balloon and were blown into sparks.... I presume we must have been upwards of a mile from the earth.... How long we were descending I have not the slightest idea, but two minutes must have been the outside.... We now saw the houses, the roofs of which appeared advancing to meet us, and the next instant, as we dashed by their summits, the words, "Hold hard!" burst simultaneously from all the party.... We were all directly thrown out of the car along the ground, and, incomprehensible as it now appears to me, n.o.body was seriously hurt."
But "not so incomprehensible, after all," will be the verdict of all who compare the above narrative with the ascents given in a foregoing account of how Wise had fared more than once when his balloon had burst.
For, as will be readily guessed, the balloon had in this case also burst, owing to the release of the upper valve being delayed too long, and the balloon had in the natural way transformed itself into a true parachute. Moreover, the fall, which, by Albert Smith"s own showing, was that of about a mile in two minutes, was not more excessive than one which will presently be recorded of Mr. Glaisher, who escaped with no material injury beyond a few bruises.
One fact has till now been omitted with regard to the above sensational voyage, namely, the name of the pa.s.senger who, sitting in the ring, was the first to point out the imminent danger of the balloon. This individual was none other than Mr. Henry c.o.xwell, the second, indeed, of the two who were mentioned in the opening paragraph of this chapter as marking the road of progress which it is the scope of these pages to trace, and to whom we must now formally introduce our readers.
This justly famous sky pilot, whose practical acquaintance with ballooning extends over more than forty years, was the son of a naval officer residing near Chatham, and in his autobiography he describes enthusiastically how, a lad of nine years old, he watched through a sea telescope a balloon, piloted by Charles Green, ascend from Rochester and, crossing the Thames, disappear in distance over the Ess.e.x flats. He goes on to describe how the incident started him in those early days on boyish endeavours to construct fire balloons and paper parachutes. Some years later his home, on the death of his father, being transferred to Eltham, he came within frequent view of such balloons as, starting from the neighbourhood of London, will through the summer drift with the prevailing winds over that part of Kent. And it was here that, ere long, he came in at the death of another balloon of which Green was in charge.
And from this time onwards the schoolboy with the strange hobby was constantly able to witness the flights and even the inflations of those ships of the air, which, his family a.s.sociations notwithstanding took precedence of all boyish diversions.
His elder brother, now a naval officer, entirely failed to divert his aspirations into other channels, and it was when the boy had completed sixteen summers that an aeronautic enterprise attracted not only his own, but public attention also. It was the building of a mammoth balloon at Vauxhall under the superintendence of Mr. Green. The launching of this huge craft when completed was regarded as so great an occasion that the young c.o.xwell, who had by this time obtained a commercial opening abroad, was allowed, at his earnest entreaty, to stay till the event had come off, and fifty years after the hardened sky sailor is found describing with a boyish enthusiasm how thirty-six policemen were needed round that balloon; how enormous weights were attached to the cordage, only to be lifted feet above the ground; while the police were compelled to pa.s.s their staves through the meshes to prevent the cords cutting their hands. At this ascent Mr. Hollond was a pa.s.senger, and by the middle of the following November all Europe was ringing with the great Na.s.sau venture.
Commercial business did not suit the young c.o.xwell, and at the age of one-and-twenty we find him trying his hand at the profession of surgeon-dentist, not, however, with any prospect of its keeping him from the longing of his soul, which grew stronger and stronger upon him. It was not till the summer of 1844 that Mr. Hampton, giving an exhibition from the White Conduit Gardens, Pentonville, offered the young man, then twenty-five years old, his first ascent.
In after years c.o.xwell referred to his first sensations in characteristic language, contrasting them with the experiences of the mountaineer. "In Alpine travels," he says, "the process is so slow, and contact with the crust of the earth so palpable, that the traveller is gradually prepared for each successive phase of view as it presents itself. But in the balloon survey, cities, villages, and vast tracts for observation spring almost magically before the eye, and change in aspect and size so pleasingly that bewilderment first and then unbounded admiration is sure to follow."
The ice was now fairly broken, and, not suffering professional duties to be any hindrance, c.o.xwell began to make a series of ascents under the leadership of two rival balloonists, Gale and Gypson. One voyage made with the latter he describes as leading to the most perilous descent in the annals of aerostation. This was the occasion, given above, on which Albert Smith was a pa.s.senger, and which that talented writer describes in his own fashion. He does not, however, add the fact, worthy of being chronicled, that exactly a week after the appalling adventure Gypson and c.o.xwell, accompanied by a Captain whose name does not transpire, and loaded with twice the previous weight of fireworks, made a perfectly successful night ascent and descent in the same balloon.
It is very shortly after this that we find c.o.xwell seduced into undertaking for its owners the actual management of a balloon, the property of Gale, and now to be known as the "Sylph." With this craft he practically began his career as a professional balloonist, and after a few preliminary ascents made in England, was told off to carry on engagements in Belgium.
A long series of ascents was now made on the Continent, and in the troubled state of affairs some stirring scenes were visited, not without some real adventure. One occasion attended with imminent risk occurred at Berlin in 1851. c.o.xwell relates that a Prussian labourer whom he had dismissed for bad conduct, and who almost too manifestly harboured revenge, nevertheless begged hard for a re-engagement, which, as the man was a handy fellow, c.o.xwell at length a.s.sented to. He took up three pa.s.sengers beside himself, and at an elevation of some 3,000 feet found it necessary to open the valve, when, on pulling the cord, one of the top shutters broke and remained open, leaving a free aperture of 26 inches by 12 inches, and occasioning such a copious discharge of gas that nothing short of a providential landing could save disaster. But the providential landing came, the party falling into the embrace of a fruit tree in an orchard. It transpired afterwards that the labourer had been seen to tamper with the valve, the connecting lines of which he had partially severed.
Returning to England in 1852 c.o.xwell, through the accidents inseparable from his profession, found himself virtually in possession of the field.
Green, now advanced in years, was retiring from the public life in which he had won so much fame and honour. Gale was dead, killed in an ascent at Bordeaux. Only one aspirant contested the place of public aeronaut--one Goulston, who had been Gale"s patron. Before many months, however, he too met with a balloonist"s death, being dashed against some stone walls when ascending near Manchester.
It will not be difficult to form an estimate of how entirely the popularity of the balloon was now reestablished in England, from the mere fact that before the expiration of the year c.o.xwell had been called upon to make thirty-six voyages. Some of these were from Glasgow, and here a certain coincidence took place which is too curious to be omitted. A descent effected near Milngavie took place in the same field in which Sadler, twenty-nine years before, had also descended, and the same man who caught the rope of Mr. Sadler"s balloon performed the same service once again for a fresh visitor from the skies.
The following autumn c.o.xwell, in 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 circ.u.mstances.
c.o.xwell 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, inst.i.tuted. It was the British a.s.sociation 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 Na.s.sau 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 quant.i.ty of air, brought from other levels, while the temperature of its own ma.s.s 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 pa.s.sage, 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. It is on this account that some allowance must be made for observations which will, in due place, be recorded of scientific explorers; the point to be borne in mind being that, as was mentioned in a former chapter, such observations will have to be regarded as giving readings which are somewhat too high in ascents and too low in descents.
Two forms of thermometers at extremely simple construction, yet possessed of great sensibility, will be discussed in later chapters.
The thermometers that Welsh used were undoubtedly far superior to any that were devised before his time and it is much to be regretted that they were allowed to fall into disuse. Perhaps the most important stricture on the observations that will have to be recorded is that the observers were not provided with a base station, on which account the value of results was impaired. It was not realised that it was necessary to make observations on the ground to compare with those that were being made at high alt.i.tudes.