Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/225

 viscosity is obtained. “If one assumes forhe coefficient of viscosity the order of 1019 (instead of Epstein’s 1016) and makes the supposition that the formula used by Epstein is applicable in this case, then one obtains about 20 cm. per annum for the velocity of a block in the latitude of 45°. In any case, it is shown to be possible that the continents undergo a displacement directed towards the equator under the influence of this force.”

We can combine the foregoing statements in the sentence that there is no longer any doubt as to the existence and magnitude of the force of the drift from the poles. It amounts at the maximum (in latitude 45°) to about a two- or three-millionth part of gravity, and is thus, in any case, still four times greater than the horizontal tidal forces. But since it does not vary as these do, but for millions upon millions of years works on unchanged, it is enabled to overcome the steel-like viscosity of the earth’s body in the course of geological periods, provided only that it is not less than the minimum force (which indeed we do not know) required to produce movement. Now we have already seen that the continents behave like wax and the sima like sealing-wax. The minimum force required is, in any case, very much smaller in the sima than in the sial. On that account it appears to me to be highly probable that considerable displacements of the continental blocks have actually taken place in the sima in the course of geological time as a consequence of the force of the drift from the poles. On the other hand, it seems more doubtful whether this force is sufficient to explain the equatorial mountain chains, although Epstein’s results are probably not the last word in this matter.

We can be more brief in the discussion of the forces