Page:In the high heavens.djvu/346

 the resistance offered by the air to the passage of projectiles may perhaps be over-estimated.

In the first place, it must be remembered that the analogy of artillery is hardly to the purpose, for the trajectory of the missile, if not quite horizontal, has at all events no great inclination. The consequence is, that the flight of the body is confined to the lower and denser strata of the atmosphere, where of course the resistance of the air operates much more vigorously. A cannon ball fired vertically upwards would meet with much less obstruction to its upward passage after it had passed through the lower portions of the atmosphere, and the amount of that obstruction would be diminished with every increase in the body's altitude. It is therefore plain that if a volcano were projecting missiles in a vertical direction, as the terrestrial theory of meteorites supposes, the resistance of the air would be much less effective than if the missile were projected in any direction largely inclined to the vertical.

There is also another consideration. It is well known that on the top of a mountain the air is less dense than at the foot. Suppose, therefore, the volcanic discharge takes place from the summit of a lofty mountain peak, the missile will then start on its vertical journey exposed to a resistance not very considerable at the commencement and lessening as each additional foot of elevation is attained. Now there is good reason to believe that in those primeval periods, when the meteorites were launched from the earth, the mountains were more elevated than they are at present. Here, again, I fear I shall have to reckon with the uniformitarian geologist. He will probably dispute this contention, and if he does so I confess that I know no direct facts which I can urge in support of my belief