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adland on which he hoped to alight was not in the direction of the wind's course。 Resolved； however； on gratifying the crowd； Mr。 Hampton ascended rapidly； and then with equal expedition commenced a precipitate descent； which he accomplished with skill and without mishap。 But the wind was still boisterous； and the balloon sped onward along the ground towards fresh danger unforeseen； and perhaps not duly reckoned with。 Ahead was a cottage； the chimney of which was on fire。 A balloonist in these circumstances is apt to think little of a single small object in his way； knowing how many are the chances of missing or of successfully negotiating any such obstacle。 The writer on one occasion was； in the judgment of onlookers below； drifting in dangerous proximity to the awful Cwmavon stack in Glamorganshire； then in full blast； yet it was a fact that that vast vent of flame and smoke passed almost unheeded by the party in the descending car。 It may have been thus； also； with Mr。 Hampton； who only fully realised his danger when his balloon blew up 〃with an awfully grand explosion；〃 and he was reduced to the extremity of jumping for his life； happily escaping the mass of burning silk and ropes。
The awful predicament of falling into the sea； which has been illustrated already； and which will recur again in these pages； was ably and successfully met by Mr。 Cunningham； who made an afternoon ascent from the Artillery Barracks at Clevedon； reaching Snake Island at nightfall； where； owing to the gathering darkness； he felt constrained to open his valve。 He quickly commenced descending into the sea； and when within ten feet of the water； turned the 〃detaching screw〃 which connected the car with the balloon。 The effect of this was at once to launch him on the waves； but； being still able to keep control over the valve； he allowed just enough gas to remain within the silk to hold the balloon above water。 He then betook himself to the paddles with which his craft was provided； and reached Snake Island with the balloon in tow。 Here he seems to have found good use for a further portion of his very complete equipment； for； lighting a signal rocket； he presently brought a four…oared gig to his succour from Portsmouth Harbour。
The teaching of the above incident is manifest enough。 If it should be contemplated to use the balloon for serious or lengthened travel anywhere within possible reach of the sea…boardand this must apply to all parts of the British Islesit must become a wise precaution； if not an absolute necessity； to adopt some form of car that would be of avail in the event of a fall taking place in the sea。 Sufficient confirmation of this statement will be shortly afforded by a memorable voyage accomplished during the partnership of Messrs。 Glaisher and Coxwell； one which would certainly have found the travellers in far less jeopardy had their car been convertible into a boat。 We have already seen how essential Wise considered this expedient in his own bolder schemes； and it may further be mentioned here that modern air ships have been designed with the intention of making the water a perfectly safe landing。
The ballooning exploits which； however； we have now to recount had quite another and more special object consistently in viewthat of scientific investigation； and we would here premise that the proper appreciation of these investigations will depend on a due understanding of the attendant circumstances； as also of the constant characteristic behaviour of balloons； whether despatched for mere travel or research。
First let us regard the actual path of a balloon in space when being manoeuvred in the way we read of in Mr。 Glaisher's own accounts。 This part is in most cases approximately indicated in that most attractive volume of his entitled； 〃Travels in the Air；〃 by diagrams giving a sectional presentment of his more important voyages； but a little commonplace consideration may take the place of diagrams。
It has been common to assert that a balloon poised in space is the most delicate balance conceivable。 Its intrinsic weight must be exactly equal to the weight of the air it displaces； and since the density of the air decreases according to a fixed law； amounting； approximately； to a difference in barometric reading of 0。1 inch for every 90 feet； it follows； theoretically； that if a balloon is poised at 1；000 feet above sea level； then it would not be in equilibrium at any other height； so long as its weight and volume remain the same。 If it were 50 feet higher it must commence descending； and； if lower； then it must ascend till it reaches its true level； and； more than that； in the event of either such excursion mere impetus would carry it beyond this level； about which it would oscillate for a short time； after the manner of the pendulum。 This is substantially true； but it must be taken in connection with other facts which have a far greater influence on a balloon's position or motion。
For instance； in the volume just referred to it is stated by M。 Gaston Tissandier that on one occasion when aloft he threw overboard a chicken bone； and； immediately consulting a barometer； had to admit on 〃clearest evidence that the bone had caused a rise of from twenty to thirty yards； so delicately is a balloon equipoised in the air。〃 Here； without pausing to calculate whether the discharge of an ounce or so would suffice to cause a large balloon to ascend through ninety feet； it may be pointed out that the record cannot be trustworthy； from the mere fact that a free balloon is from moment to moment being subjected to other potent influences； which necessarily affect its position in space。 In daytime the sun's influence is an all…important factor； and whether shining brightly or partially hidden by clouds； a slight difference in obscuration will have a ready and marked effect on the balloon's altitude。 Again； a balloon in transit may pass almost momentarily from a warmer layer of air to a colder； or vice versa； the plane of demarcation between the two being very definite and abrupt； and in this case altitude is at once affected； or； yet again； there are the descending and ascending currents； met with constantly and unexpectedly； which have to be reckoned with。
Thus it becomes a fact that a balloon's vertical course is subjected to constant checks and vicissitudes from a variety of causes； and these will have to be duly borne in mind when we are confronted with the often surprising results and readings which are supplied by scientific observers。 With regard to the close proximity； without appreciable intermingling； of widely differing currents； it should be mentioned that explorers have found in regions where winds of different directions pass each other that one air stream appears actually to drag against the surface of the other； as though admitting no interspace where the streams might mingle。 Indeed； trustworthy observers have stated that even a hurricane can rage over a tranquil atmosphere with a sharply defined surface of demarcation between calm and storm。 Thus； to quote the actual words of Charles Darwin； than whom it is impossible to adduce a more careful witness； we find him recording how on mountain hei