remarks being admitted, the cannon ought to be pointed to the zenith of the place. Its fire, therefore, will be perpendicular to the plane of the horizon; and the projectile will soonest pass beyond the range of the terrestrial attraction. But, in order that the moon should reach the zenith of a given place, it is necessary that the place should not exceed in latitude the declination of the luminary; in other words, it must be comprised within the degrees 0° and 28° of lat. N. or S. In every other spot the fire must necessarily be oblique, which would seriously militate against the success of the experiment. 

 As to the sixth question, “What place will the moon occupy in the heavens at the moment of the projectile’s departure?” 

 Answer.—At the moment when the projectile shall be discharged into space, the moon, which travels daily forward 13° 10′ 35″, will be distant from the zenith point by four times that quantity, i. e. by 52° 41′ 20″, a space which corresponds to the path which she will describe during the entire journey of the projectile. But, inasmuch as it is equally necessary to take into account the deviation which the rotary motion of the earth will impart to the shot, and as the shot cannot reach the moon until after a deviation equal to 16 radii of the earth, which, calculated upon the moon’s orbit, are equal to about eleven degrees, it becomes necessary to add these eleven degrees to those which express the retardation of the moon just mentioned: that is to say, in round numbers, about sixty-four degrees. Consequently, at the moment of firing the visual radius applied to the moon will describe, with the vertical line of the place, an angle of sixty-four degrees. 

 These are our answers to the questions proposed to the Observatory of Cambridge by the members of the Gun Club:— 

 To sum up— 

 1st. The cannon ought to be planted in a country situated between 0° and 28° of N. or S. lat. 

 2nd. It ought to be pointed directly toward the zenith of the place. 

 3rd. The projectile ought to be propelled with an initial velocity of 12,000 yards per second. 

 4th. It ought to be discharged at 10hrs. 46m. 40sec. of the 1st of December of the ensuing year. 

 5th. It will meet the moon four days after its discharge, precisely at midnight on the 4th of December, at the moment of its transit across the zenith. 

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