With a rapidity of 12,000 yards the projectile will cross that in five seconds, and this time will be short enough to make the resistance of the medium insignificant.

Let us now pass to the attraction of the earth--that is to say, to the weight of the projectile.

We know that that weight diminishes in an inverse ratio to the square of distances--in fact, this is what physics teach us: when a body left to itself falls on the surface of the earth, it falls 15 feet in the first second, and if the same body had to fall 257,542 miles--that is to say, the distance between the earth and the moon--its fall would be reduced to half a line in the first second.

That is almost equivalent to immobility.

The question is, therefore, how progressively to overcome this law of gravitation.