The Moon-Voyage, page 45
CHAPTER XVI.
THE SOUTHERN HEMISPHERE.
The projectile had just escaped a terrible danger, a danger quiteunforeseen. Who would have imagined such a meeting of asteroids? Thesewandering bodies might prove serious perils to the travellers. They wereto them like so many rocks in the sea of ether, which, less fortunatethan navigators, they could not avoid. But did these adventurers ofspace complain? No, as Nature had given them the splendid spectacle of acosmic meteor shining by formidable expansion, as this incomparabledisplay of fireworks, which no Ruggieri could imitate, had lighted for afew seconds the invisible nimbus of the moon. During that rapid peep,continents, seas, and forests had appeared to them. Then the atmospheredid give there its life-giving particles? Questions still not solved,eternally asked by American curiosity.
It was then 3.30 p.m. The bullet was still describing its curve roundthe moon. Had its route again been modified by the meteor? It was to befeared. The projectile ought, however to describe a curve imperturbablydetermined by the laws of mechanics. Barbicane inclined to the opinionthat this curve would be a parabola and not an hyperbola. However, ifthe parabola was admitted, the bullet ought soon to come out of the coneof shadow thrown into the space on the opposite side to the sun. Thiscone, in fact, is very narrow, the angular diameter of the moon is sosmall compared to the diameter of the orb of day. Until now theprojectile had moved in profound darkness. Whatever its speed hadbeen--and it could not have been slight--its period of occultationcontinued. That fact was evident, but perhaps that would not have beenthe case in a rigidly parabolical course. This was a fresh problem whichtormented Barbicane's brain, veritably imprisoned as it was in a web ofthe unknown which he could not disentangle.
Neither of the travellers thought of taking a minute's rest. Eachwatched for some unexpected incident which should throw a new light ontheir uranographic studies. About five o'clock Michel distributed tothem, by way of dinner, some morsels of bread and cold meat, which wererapidly absorbed, whilst no one thought of leaving the port-light, thepanes of which were becoming incrusted under the condensation of vapour.
About 5.45 p.m., Nicholl, armed with his telescope, signalised upon thesouthern border of the moon, and in the direction followed by theprojectile, a few brilliant points outlined against the dark screen ofthe sky. They looked like a succession of sharp peaks with profiles in atremulous line. They were rather brilliant. The terminal line of themoon looks the same when she is in one of her octants.
They could not be mistaken. There was no longer any question of a simplemeteor, of which that luminous line had neither the colour nor themobility, nor of a volcano in eruption. Barbicane did not hesitate todeclare what it was.
"The sun!" he exclaimed.
"What! the sun!" answered Nicholl and Michel Ardan.
"Yes, my friends, it is the radiant orb itself, lighting up the summitof the mountains situated on the southern border of the moon. We areevidently approaching the South Pole!"
"After having passed the North Pole," answered Michel. "Then we havebeen all round our satellite."
"Yes, friend Michel."
"Then we have no more hyperbolas, no more parabolas, no more open curvesto fear!"
"No, but a closed curve."
"Which is called--"
"An ellipsis. Instead of being lost in the interplanetary spaces it ispossible that the projectile will describe an elliptical orbit round themoon."
"Really!"
"And that it will become its satellite."
"Moon of the moon," exclaimed Michel Ardan.
"Only I must tell you, my worthy friend, that we are none the less lostmen on that account!"
"No, but in another and much pleasanter way!" answered the carelessFrenchman, with his most amiable smile.
President Barbicane was right. By describing this elliptical orbit theprojectile was going to gravitate eternally round the moon like asub-satellite. It was a new star added to the solar world, a microcosmpeopled by three inhabitants, whom want of air would kill before long.Barbicane, therefore, could not rejoice at the position imposed on thebullet by the double influence of the centripetal and centrifugalforces. His companions and he were again going to see the visible faceof the disc. Perhaps their existence would last long enough for them toperceive for the last time the full earth superbly lighted up by therays of the sun! Perhaps they might throw a last adieu to the globe theywere never more to see again! Then their projectile would be nothing butan extinct mass, dead like those inert asteroids which circulate in theether. A single consolation remained to them: it was that of seeing thedarkness and returning to light, it was that of again entering the zonesbathed by solar irradiation!
In the meantime the mountains recognised by Barbicane stood out more andmore from the dark mass. They were Mounts Doerfel and Leibnitz, whichstand on the southern circumpolar region of the moon.
All the mountains of the visible hemisphere have been measured withperfect exactitude. This perfection will, no doubt, seem astonishing,and yet the hypsometric methods are rigorous. The altitude of the lunarmountains may be no less exactly determined than that of the mountainsof the earth.
The method generally employed is that of measuring the shadow thrown bythe mountains, whilst taking into account the altitude of the sun at themoment of observation. This method also allows the calculating of thedepth of craters and cavities on the moon. Galileo used it, and sinceMessrs. Boeer and Moedler have employed it with the greatest success.
Another method, called the tangent radii, may also be used for measuringlunar reliefs. It is applied at the moment when the mountains formluminous points on the line of separation between light and darknesswhich shine on the dark part of the disc. These luminous points areproduced by the solar rays above those which determine the limit of thephase. Therefore the measure of the dark interval which the luminouspoint and the luminous part of the phase leave between them givesexactly the height of the point. But it will be seen that this methodcan only be applied to the mountains near the line of separation ofdarkness and light.
A third method consists in measuring the profile of the lunar mountainsoutlined on the background by means of a micrometer; but it is onlyapplicable to the heights near the border of the orb.
In any case it will be remarked that this measurement of shadows,intervals, or profiles can only be made when the solar rays strike themoon obliquely in relation to the observer. When they strike herdirectly--in a word, when she is full--all shadow is imperiouslybanished from her disc, and observation is no longer possible.
Galileo, after recognising the existence of the lunar mountains, was thefirst to employ the method of calculating their heights by the shadowsthey throw. He attributed to them, as it has already been shown, anaverage of 9,000 yards. Hevelius singularly reduced these figures, whichRiccioli, on the contrary, doubled. All these measures were exaggerated.Herschel, with his more perfect instruments, approached nearer thehypsometric truth. But it must be finally sought in the accounts ofmodern observers.
Messrs. Boeer and Moedler, the most perfect selenographers in the wholeworld, have measured 1,095 lunar mountains. It results from theircalculations that 6 of these mountains rise above 5,800 metres, and 22above 4,800. The highest summit of the moon measures 7,603 metres; itis, therefore, inferior to those of the earth, of which some are 1,000yards higher. But one remark must be made. If the respective volumes ofthe two orbs are compared the lunar mountains are relatively higher thanthe terrestrial. The lunar ones form 1/70 of the diameter of the moon,and the terrestrial only form 1/140 of the diameter of the earth. For aterrestrial mountain to attain the relative proportions of a lunarmountain, its perpendicular height ought to be 6-1/2 leagues. Now thehighest is not four miles.
Thus, then, to proceed by comparison, the chain of the Himalayas countsthree peaks higher than the lunar ones, Mount Everest, Kunchinjuga, andDwalagiri. Mounts Doerfel and Leibnitz, on the moon, are as high asJewahir in the same chain. Newton, Casatus, Curtius, Short, Tycho,Clavius, Blancanus, Endymion, the principal summits of Caucasus and theApennines, are higher than Mont Blanc. The mountains equal to Mont Blancare Moret, Theophylus, and Catharnia; to Mount Rosa, Piccolomini,Werner, and Harpalus; to Mount Cervin, Macrobus, Eratosthenes,Albateque, and Delambre; to the Peak of Teneriffe, Bacon, Cysatus,Philolaus, and the Alps; to Mount Perdu, in the Pyrenees, Roemer andBoguslawski; to Etna, Hercules, Atlas, and Furnerius.
Such are the points of comparison that allow the appreciation of thealtitude of lunar mountains. Now the trajectory followed by theprojectile dragged it precisely towards that mountainous region of thesouthern hemisphere where rise the finest specimens of lunar orography.
