the dominion of the air-第25章
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00 feet； at which level an air…stream from the north was encountered； but at 3；000 feet higher the wind again changed to a current from the N。N。W。 At the height； then； of little more than half a mile； these upper currents were travelling leisurely； but what was more noteworthy was their humidity； which greatly increased with altitude； and a fact which may often be noted here obtruded itself； namely； when the aeronauts were at the upperlimits of the east wind； flat…bottomed cumulus clouds were floating at their level。 These clouds were entirely within the influence of the upper or north wind； so that their under sides were in contact with the east wind； i。e。 with a much drier air； which at once dissipated all vapour in contact with it； and thus presented the appearance of flat…bottomed clouds。 It is a common experience to find the lower surface of a cloud mowed off flat by an east wind blowing beneath it。
At the end of June a voyage from Wolverton was accomplished； which yielded remarkable results of much real value and interest。 The previous night had been perfectly calm； and through nearly the whole morning the sun shone in a clear blue sky； without a symptom of wind or coming change。 Shortly before noon； however； clouds appeared aloft； and the sky assumed an altered aspect。 Then the state of things quickly changed。 Wind currents reached the earth blowing strongly； and the half…filled balloon began to lurch to such an extent that the inflation could only with difficulty be proceeded with。 Fifty men were unable to hold it in sufficient restraint to prevent rude bumping of the car on the ground； and when； at length； arrangements were complete and release effected； rapid discharge of ballast alone saved collision with neighbouring buildings。
It was now that the disturbance overhead came under investigation； and； considering the short period it had been in progress； proved most remarkable； the more so the further it was explored。 At 4；000 feet they plunged into the cloud canopy； through which as it was painfully cold； they； sought to penetrate into the clear above； feeling confident of finding themselves； according to their usual experience； in bright blue sky； with the sun brilliantly shining。 On the contrary； however； the region they now entered was further obscured with another canopy of cloud far up。 It was while they were traversing this clear interval that a sound unwonted in balloon travel assailed their ears。 This was the 〃sighing； or rather moaning； of the wind as preceding a storm。〃 Rustling of the silk within the cordage is often heard aloft； being due to expansion of gas or similar cause； but the aeronauts soon convinced themselves that what they heard was attributable to nothing else than the actual conflict of air currents beneath。 Then they reached foga dry fogand； passing through it； entered a further fog； but wetting this time； and within the next 1；000 feet they were once again in fog that was dry； and then； reaching three miles high and seeing struggling sunbeams； they looked around and saw cloud everywhere； below； above； and far clouds on their own level。 The whole sky had filled in most completely since the hours but recently passed； when they had been expatiating on the perfect serenity of the empty heavens。
Still they climbed upwards； and in the next 2；000 feet had entered further fog； dry at first； but turning wetter as they rose。 At four miles high they found themselves on a level with clouds； whose dark masses and fringed edges proved them to be veritable rain clouds； and； while still observing them； the fog surged up again and shut out the view； and by the time they had surmounted it they were no less than 23；000 feet up； or higher than the loftiest of the Andes。 Even here； with cloud masses still piling high overhead； the eager observer； bent on further quests； was for pursuing the voyage； but Mr。 Coxwell interposed with an emphatic； 〃Too short of sand！〃 and the downward journey had to be commenced。 Then phenomena similar to those already described were experienced againfog banks （sometimes wet； sometimes dry）； rain showers； and cloud strata of piercing cold。 Presently； too； a new wonder for a midsummer afternoona snow scene all around； and spicules of ice settling and remaining frozen on the coatsleeve。 Finally dropping to earth helplessly through the last 5；000 feet； with all ballast spent； Ely Cathedral was passed at close quarters； yet even that vast pile was hidden in the gloom that now lay over all the land。
It was just a month later； and day broke with thoroughly dirty weather； a heavy sky； and falling showers。 This was the day of all others that Mr。 Glaisher was waiting for； having determined on making special investigations concerning the formation of rain in the clouds themselves。 It had long been noticed that； in an ordinary way； if there be two rain gauges placed； one near the surface of the ground； and another at a somewhat higher elevation； then the lower gauge will collect most water。 Does； then； rain condense in some appreciable quantity out of the lowest level？ Again； during rain； is the air saturated completely； and what regulates the quality of rainfall； for rain sometimes falls in large drops and sometimes in minute particles？ These were questions which Mr。 Glaisher sought to solve； and there was another。
Charles Green had stated as his conviction that whenever rain was falling from an overcast sky there would always be found a higher canopy of cloud over…hanging the lower stratum。 On the day； then； which we are now describing； Mr。 Glaisher wished to put this his theory to the test； and； if correct； then he desired to measure the space between the cloud layers； to gauge their thickness； and to see if above the second stratum the sun was shining。 The main details of the ascent read thus：
In ten seconds they were in mist； and in ten seconds more were level with the cloud。 At 1；200 feet they were out of the rain； though not yet out of the cloud。 Emerging from the lower cloud at 2；300 feet； they saw； what Green would have foretold； an upper stratum of dark cloud above。 Then they made excursions up and down； trying high and low to verify these conditions； and passing through fogs both wet and dry； at last drifting earthward； through squalls of wind and rain with drops as large as fourpenny pieces； to find that on the ground heavy wet had been ceaselessly falling。
A day trip over the eastern suburbs of London in the same year seems greatly to have impressed Mr。 Glaisher。 The noise of London streets as heard from above has much diminished during the last fifteen years' probably owing to the introduction of wood paving。 But； forty years ago； Mr。 Glaisher describes the deep sound of London as resembling the roar of the sea； when at a mile high； while at greater elevations it was heard at a murmuring noise。 But the view must have been yet more striking than the hearing； for in one direction the white cliffs from Margate to Dover were visible； while Brighton and the sea beyond were sighted； and again all the coast line up to Yarmouth yet the atmosphere that day； one might have thought； should have been in turmoil； by reason of a conflict of aircurrents； for； within two miles of the earth； the wind was from the east； between two and three miles high it was exactly opposite； being from the west； but at three miles it was N。E。； while； higher； it was again directly opposite； or S。W。
During his researches so far Mr。 Glaisher had found much that was anomalous in the way of the winds； and in other elements of weather。 He was destined to find much more。 It had been commonly accepted that the temperature of the air decreases at the average rate of 10 degrees for every 300 feet of elevation； and various computations； as； for example； those which relate to the co…efficient of refraction； have been founded on this basis； but Mr。 Glaisher soon established that the above generalisation had to be much modified。 The following； gathered from his notes is a typical example of such surprises as the aeronaut with due instrumental equipment may not unfrequently meet with。
It was the 12th of January； 1864； with an air…current on the ground from the S。E。； of temperature 41 degrees；； which very slowly decreased up to 1；600 feet when a warm S。W。 current was met with； and at 3；000 feet the temperature was 3 1/2 degrees higher than on the earth。 Above the S。W。 stream the air became dry； and here the temperature decreased reasonably and consistently with altitude； while fine snow was found falling out of this upper space into the warmer stream below。 Mr。 Glaisher discusses the peculiarity and formation of this stream in terms which will repay consideration。
〃The meeting with this S。W。 current is of the highest importance； for it goes far to explain why England possesses a winter temperature so much higher than is due to her northern latitude。 Our high winter temperature has hitherto been mostly referred to the influence of the Gulf Stream。 Without doubting the influence of this natural agent； it is necessary to add the effect of a parallel atmospheric current to the oceanic current coming from the same regiona true aerial Gulf Stream。 This great energetic current meets with no obstruction in coming to us； or to Norway； but passes over the level Atlantic without interruption from mountains。 It cannot； however； reach France without crossing Spain and the lofty range of the Pyrenees； and the effect of these cold mountains in reducing its temperature is so great that the former country derives but little warmth from it。〃
An ascent from Woolwich； arranged as near the equinox of that year as could be managed； supplied some further remarkable results。 The temperature； which was 45 degrees to begin with； at 4。7 p。m。； crept down fairly steadily till 4；000 feet altitude was registered； when； in a region of warm fog； it commenced rising abruptly； and at 7；500 feet； in blue sky； stood at the same reading as when the balloon had risen only 1；500 feet。 Then； amid many anomalous vicissitudes； the most curious； perhaps； was that recorded late in the afternoon； when； at 10；000 feet； the air was actually warmer than when the ascent began。
That the temperature of the upper air commonly commences to rise after nightfall as the warmth radiated through day hours off the earth collects aloft； is a fact well known to the balloonist； and Mr。 Glaisher carried out with considerable success a well…arranged programme for investigating the facts of the case。 Starting from Windsor on an afternoon of late May； he so arranged matters that his departure from earth took place about an hour and three quarters before sunset； his intention being to rise to a definite height； and with as uniform a speed as possible to time his descent so as to reach earth at the moment of sundown； and then to re…ascend and descend again m a precisely similar manner during an hour and three…quarters after sunset； taking observations all the way。 Ascending for the first flight； he left a temperature of 58 degrees on the earth； and found it 55 degrees at 1；200 feet； then 43 degrees at 3；600 feet； and 29 1/2 degrees at the culminating point of 6；200 feet。 Then； during the descent； the temperature increased； though not un
