Whilst these “rivers in the ocean” are flowing more or less rapidly toward the Arctic regions, there are undercurrents moving slowly but irresistibly toward the equator, or at least in a direction to restore the equilibrium of waters. That these undercurrents come from the poles is already demonstrated by the thermometer. At certain depths under the equator the temperature is as low as 35° or 36° F. This low temperature could not be maintained unless supplied from the Polar regions. Fresh water freezes at 32° and salt water, that is sea water, at about 27°, according to the density. In many places north of England, Dr. Carpenter found the lower depths at a temperature of about 29°. He speaks of an ocean river 2,000 feet deep, colder than the freezing point of fresh water. Why could not this low temperature be maintained without supposing a supply from the Polar regions? The temperature of the earth’s crust twenty or thirty feet from the surface is quite uniform at 50° to 55° all over the temperate zones. At that depth—say thirty feet—it is not deep enough to be influenced by “the internal heat” of the earth, which we experience in going down into mines, or which shows itself in the hot water from very deep springs, and yet it is sufficiently covered so as not to be influenced by seasonable changes. The water would naturally take the temperature of the earth’s crust. This has been proven in the case of the Mediterranean Sea. This body of water is shut off from the general circulatory system by the Strait of Gibraltar, which is so shallow at its outlet that no communication between the deep water of the Mediterranean and the Atlantic can possibly take place. This great “middle earth sea” is at some places 11,000 to 12,000 feet deep. And yet Dr. Carpenter found the temperature in August and September 78° at the surface; and by going down with the thermometer the heat gradually diminished, until at the depth of 600 feet the temperature was 55°. From this point, curious as it may appear, there was no change in heat until the bottom was reached. Whatever was the temperature at 600 feet it was the same all the way down. He then ascertained that the temperature of the earth’s crust in that region was 54° and 55°. This shows pretty clearly that depth of water alone does not produce the coldness found in the seas having connection with the Polar regions.