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1REPLY FROM THE OBSERVATORY OF CAMBRIDGE Barbicane, however, lost not one moment amid all the enthusiasm of which he had
2become the object. His first care was to reassemble his colleagues in the board-room of the Gun Club. There, after some
3discussion, it was agreed to consult the astronomers regarding the astronomical part of the enterprise. Their reply once
4ascertained, they could then discuss the mechanical means, and nothing should be wanting to ensure the success of this
5great experiment. A note couched in precise terms, containing special interrogatories, was then drawn up and addressed
6to the Observatory of Cambridge in Massachusetts. This city, where the first university of the United States was
7founded, is justly celebrated for its astronomical staff. There are to be found assembled all the most eminent men of
8science. Here is to be seen at work that powerful telescope which enabled Bond to resolve the nebula of Andromeda, and
9Clarke to discover the satellite of Sirius. This celebrated institution fully justified on all points the confidence
10reposed in it by the Gun Club. So, after two days, the reply so impatiently awaited was placed in the hands of President
11Barbicane. It was couched in the following terms: The Director of the Cambridge Observatory to the President of the Gun
12Club at Baltimore. CAMBRIDGE, October 7. On the receipt of your favor of the 6th instant, addressed to the Observatory
13of Cambridge in the name of the members of the Baltimore Gun Club, our staff was immediately called together, and it was
14judged expedient to reply as follows: The questions which have been proposed to it are these-- "1. Is it possible to
15transmit a projectile up to the moon? "2. What is the exact distance which separates the earth from its satellite? "3.
16What will be the period of transit of the projectile when endowed with sufficient initial velocity? and, consequently,
17at what moment ought it to be discharged in order that it may touch the moon at a particular point? "4. At what precise
18moment will the moon present herself in the most favorable position to be reached by the projectile? "5. What point in
19the heavens ought the cannon to be aimed at which is intended to discharge the projectile? "6. What place will the moon
20occupy in the heavens at the moment of the projectile's departure?" Regarding the first question, "Is it possible to
21transmit a projectile up to the moon?" Answer.--Yes; provided it possess an initial velocity of 12,000 yards per second;
22calculations prove that to be sufficient. In proportion as we recede from the earth the action of gravitation diminishes
23in the inverse ratio of the square of the distance; that is to say, at three times a given distance the action is nine
24times less. Consequently, the weight of a shot will decrease, and will become reduced to zero at the instant that the
25attraction of the moon exactly counterpoises that of the earth; that is to say at 47/52 of its passage. At that instant
26the projectile will have no weight whatever; and, if it passes that point, it will fall into the moon by the sole effect
27of the lunar attraction. The theoretical possibility of the experiment is therefore absolutely demonstrated; its success
28must depend upon the power of the engine employed. As to the second question, "What is the exact distance which
29separates the earth from its satellite?" Answer.--The moon does not describe a circle round the earth, but rather an
30ellipse, of which our earth occupies one of the foci; the consequence, therefore, is, that at certain times it
31approaches nearer to, and at others it recedes farther from, the earth; in astronomical language, it is at one time in
32apogee, at another in perigee. Now the difference between its greatest and its least distance is too considerable to be
33left out of consideration. In point of fact, in its apogee the moon is 247,552 miles, and in its perigee, 218,657 miles
34only distant; a fact which makes a difference of 28,895 miles, or more than one-ninth of the entire distance. The
35perigee distance, therefore, is that which ought to serve as the basis of all calculations. To the third question:--
36Answer.--If the shot should preserve continuously its initial velocity of 12,000 yards per second, it would require
37little more than nine hours to reach its destination; but, inasmuch as that initial velocity will be continually
38decreasing, it will occupy 300,000 seconds, that is 83hrs. 20m. in reaching the point where the attraction of the earth
39and moon will be in equilibrio. From this point it will fall into the moon in 50,000 seconds, or 13hrs. 53m. 20sec. It
40will be desirable, therefore, to discharge it 97hrs. 13m. 20sec. before the arrival of the moon at the point aimed at.
41Regarding question four, "At what precise moment will the moon present herself in the most favorable position, etc.?"
42Answer.--After what has been said above, it will be necessary, first of all, to choose the period when the moon will be
43in perigee, and also the moment when she will be crossing the zenith, which latter event will further diminish the
44entire distance by a length equal to the radius of the earth, i. e. 3,919 miles; the result of which will be that the
45final passage remaining to be accomplished will be 214,976 miles. But although the moon passes her perigee every month,
46she does not reach the zenith always at exactly the same moment. She does not appear under these two conditions
47simultaneously, except at long intervals of time. It will be necessary, therefore, to wait for the moment when her
48passage in perigee shall coincide with that in the zenith. Now, by a fortunate circumstance, on the 4th of December in
49the ensuing year the moon will present these two conditions. At midnight she will be in perigee, that is, at her
50shortest distance from the earth, and at the same moment she will be crossing the zenith. On the fifth question, "At
51what point in the heavens ought the cannon to be aimed?" Answer.--The preceding remarks being admitted, the cannon ought
52to be pointed to the zenith of the place. Its fire, therefore, will be perpendicular to the plane of the horizon; and
53the projectile will soonest pass beyond the range of the terrestrial attraction. But, in order that the moon should
54reach the zenith of a given place, it is necessary that the place should not exceed in latitude the declination of the
55luminary; in other words, it must be comprised within the degrees 0° and 28° of lat. N. or S. In every other spot the
56fire must necessarily be oblique, which would seriously militate against the success of the experiment. As to the sixth
57question, "What place will the moon occupy in the heavens at the moment of the projectile's departure?" Answer.--At the
58moment when the projectile shall be discharged into space, the moon, which travels daily forward 13° 10′ 35″, will be
59distant from the zenith point by four times that quantity, i. e. by 52° 41′ 20″, a space which corresponds to the path
60which she will describe during the entire journey of the projectile. But, inasmuch as it is equally necessary to take
61into account the deviation which the rotary motion of the earth will impart to the shot, and as the shot cannot reach
62the moon until after a deviation equal to 16 radii of the earth, which, calculated upon the moon's orbit, are equal to
63about eleven degrees, it becomes necessary to add these eleven degrees to those which express the retardation of the
64moon just mentioned: that is to say, in round numbers, about sixty-four degrees. Consequently, at the moment of firing
65the visual radius applied to the moon will describe, with the vertical line of the place, an angle of sixty-four
66degrees. These are our answers to the questions proposed to the Observatory of Cambridge by the members of the Gun
67Club:-- To sum up-- 1st. The cannon ought to be planted in a country situated between 0° and 28° of N. or S. lat. 2nd.
68It ought to be pointed directly toward the zenith of the place. 3rd. The projectile ought to be propelled with an
69initial velocity of 12,000 yards per second. 4th. It ought to be discharged at 10hrs. 46m. 40sec. of the 1st of December
70of the ensuing year. 5th. It will meet the moon four days after its discharge, precisely at midnight on the 4th of
71December, at the moment of its transit across the zenith. The members of the Gun Club ought, therefore, without delay,
72to commence the works necessary for such an experiment, and to be prepared to set to work at the moment determined upon;
73for, if they should suffer this 4th of December to go by, they will not find the moon again under the same conditions of
74perigee and of zenith until eighteen years and eleven days afterward. The staff of the Cambridge Observatory place
75themselves entirely at their disposal in respect of all questions of theoretical astronomy; and herewith add their
76congratulations to those of all the rest of America. For the Astronomical Staff, J. M. BELFAST, Director of the
77Observatory of Cambridge.
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