The Moon-Voyage Read online

  CHAPTER IV.

  ANSWER FROM THE CAMBRIDGE OBSERVATORY.

  In the meantime Barbicane did not lose an instant amidst the enthusiasmof which he was the object. His first care was to call together hiscolleagues in the board-room of the Gun Club. There, after a debate,they agreed to consult astronomers about the astronomical part of theirenterprise. Their answer once known, they would then discuss themechanical means, and nothing would be neglected to assure the successof their great experiment.

  A note in precise terms, containing special questions, was drawn up andaddressed to the observatory of Cambridge in Massachusetts. This town,where the first University of the United States was founded, is justlycelebrated for its astronomical staff. There are assembled the greatestmen of science; there is the powerful telescope which enabled Bond toresolve the nebula of Andromeda and Clarke to discover the satellite ofSirius. This celebrated institution was, therefore, worthy in every wayof the confidence of the Gun Club.

  After two days the answer, impatiently awaited, reached the hands ofPresident Barbicane.

  It ran as follows:--

  "_The Director of the Cambridge Observatory to the President of the GunClub at Baltimore_.

  "On the receipt of your favour of the 6th inst., addressed to theObservatory of Cambridge in the name of the members of the BaltimoreGun Club, we immediately called a meeting of our staff, who have deemedit expedient to answer as follows:--

  "The questions proposed to it were these:--

  "'1. Is it possible to send a projectile to the moon?

  "'2. What is the exact distance that separates the earth and hersatellite?

  "'3. What would be the duration of the projectile's transit to which asufficient initial speed had been given, and consequently at what momentshould it be hurled so as to reach the moon at a particular point?

  "'4. At what moment would the moon present the most favourable positionfor being reached by the projectile?

  "'5. What point in the heavens ought the cannon, destined to hurl theprojectile, be aimed at?

  "'6. What place in the heavens will the moon occupy at the moment whenthe projectile will start?'

  "Regarding question No. 1, 'Is it possible to send a projectile to themoon?'

  "Yes, it is possible to send a projectile to the moon if it is given aninitial velocity of 1,200 yards a second. Calculations prove that thisspeed is sufficient. In proportion to the distance from the earth theforce of gravitation diminishes in an inverse ratio to the square of thedistance--that is to say, that for a distance three times greater thatforce is nine times less. In consequence, the weight of the projectilewill decrease rapidly, and will end by being completely annulled at themoment when the attraction of the moon will be equal to that of theearth--that is to say, at the 47/52 of the distance. At that moment theprojectile will have no weight at all, and if it clears that point itwill fall on to the moon only by the effect of lunar gravitation. Thetheoretic possibility of the experiment is, therefore, quitedemonstrated; as to its success, that depends solely in the power of theengine employed.

  "Regarding question No. 2, 'What is the exact distance that separatesthe earth from her satellite?'

  "The moon does not describe a circle round the earth, but an ellipse, ofwhich our earth occupies one of the foci; the consequence is, therefore,that at certain times it approaches nearer to, and at others recedesfarther from, the earth, or, in astronomical language, it has its apogeeand its perigee. At its apogee the moon is at 247,552 miles from theearth, and at its perigee at 218,657 miles only, which makes adifference of 28,895, or more than a ninth of the distance. The perigeedistance is, therefore, the one that should give us the basis of allcalculations.

  "Regarding question No. 3, 'What would be the duration of theprojectile's transit to which a sufficient initial speed has been given,and consequently at what moment should it be hurled so as to reach themoon at a particular point?'

  "If the projectile kept indefinitely the initial speed of 12,000 yards asecond, it would only take about nine hours to reach its destination;but as that initial velocity will go on decreasing, it will happen,everything calculated upon, that the projectile will take 300,000seconds, or 83 hours and 20 minutes, to reach the point where theterrestrial and lunar gravitations are equal, and from that point itwill fall upon the moon in 50,000 seconds, or 13 hours, 53 minutes, and20 seconds. It must, therefore, be hurled 97 hours, 13 minutes, and 20seconds before the arrival of the moon at the point aimed at.

  "Regarding question No. 4, 'At what moment would the moon present themost favourable position for being reached by the projectile?'

  "According to what has been said above the epoch of the moon's perigeemust first be chosen, and at the moment when she will be crossing herzenith, which will still further diminish the entire distance by alength equal to the terrestrial radius--i.e., 3,919 miles; consequently,the passage to be accomplished will be 214,976 miles. But the moon isnot always at her zenith when she reaches her perigee, which is once amonth. She is only under the two conditions simultaneously at longintervals of time. This coincidence of perigee and zenith must be waitedfor. It happens fortunately that on December 4th of next year the moonwill offer these two conditions; at midnight she will be at her perigeeand her zenith--that is to say, at her shortest distance from the earthand at her zenith at the same time.

  "Regarding question No. 5, 'At what point in the heavens ought thecannon destined to hurl the projectile be aimed?'

  "The preceding observations being admitted, the cannon ought to be aimedat the zenith of the place (the zenith is the spot situated verticallyabove the head of a spectator), so that its range will be perpendicularto the plane of the horizon, and the projectile will pass the soonestbeyond the range of terrestrial gravitation. But for the moon to reachthe zenith of a place that place must not exceed in latitude thedeclination of the luminary--in other words, it must be comprisedbetween 0 deg. and 28 deg. of north or south latitude. In any other place therange must necessarily be oblique, which would seriously affect thesuccess of the experiment.

  "Regarding question No. 6, 'What place will the moon occupy In theheavens at the moment of the projectile's departure?'

  "At the moment when the projectile is hurled into space, the moon, whichtravels forward 13 deg. 10' 35" each day, will be four times as distant fromher zenith point--i.e., by 52 deg. 42' 20", a space which corresponds to thedistance she will travel during the transit of the projectile. But asthe deviation which the rotatory movement of the earth will impart tothe shock must also be taken into account, and as the projectile cannotreach the moon until after a deviation equal to sixteen radii of theearth, which, calculated upon the moon's orbit, is equal to about 11 deg.,it is necessary to add these 11 deg. to those caused by thealready-mentioned delay of the moon, or, in round numbers, 64 deg.. Thus, atthe moment of firing, the visual radius applied to the moon willdescribe with the vertical line of the place an angle of 64 deg..

  "Such are the answers to the questions proposed to the Observatory ofCambridge by the members of the Gun Club.

  "To sum up--

  "1st. The cannon must be placed in a country situated between 0 deg. and 28 deg.of north or south latitude.

  "2nd. It must be aimed at the zenith of the place.

  "3rd. The projectile must have an initial speed of 12,000 yards asecond.

  "4th. It must be hurled on December 1st of next year, at 10hrs. 46mins.40secs. p.m.

  "5th. It will meet the moon four days after its departure on December4th, at midnight precisely, at the moment she arrives at her zenith.

  "The members of the Gun Club ought, therefore, at once to commence thelabour necessitated by such an enterprise, and be ready to put them intoexecution at the moment fixed upon, for they will not find the moon inthe same conditions of perigee and zenith till eighteen years and elevendays later.

  "The staff of the Observatory of Cambridge puts itself entirely at theirdisposition for questions of theoretic astronomy, and begs to j
oin itscongratulations to those of the whole of America.

  "On behalf of the staff,

  "J.M. BELFAST,

  "_Director of the Observatory of Cambridge_."