Page:Popular Science Monthly Volume 45.djvu/491

Rh an opportunity of utilizing the tidal power. There is a continuous flow from the north (due in the first place to the Gulf Stream), estimated at between one and two hundred cubic miles per day. If a dam were thrown across, the effect would be to turn the Irish Sea into a bay and to bank the waters of the North Sea a number of feet higher on the north side of the dam than the level of the now Irish Channel on the south. From this difference of levels an unlimited quantity of power could be drawn. One can get a faint conception of the amount that would be on tap by comparing the case with that of the utilization of the energy of the Falls of Niagara. There is at present in course of construction at the falls a vast scheme of power development which will supply one hundred thousand horse power day and night all the year round. The amount of water which this will take will be insignificant compared with the total quantity going over the falls, which is roughly estimated at three hundred and fifty thousand tons per minute, and one hundred thousand horse power will be developed by about thirteen thousand tons per minute. The total power on the falls is thus some twenty-seven times the one hundred thousand horse power. This total quantity of water amounts to about one cubic mile every nine days, and the volume of water running through the Irish Channel is about one hundred and fifty cubic miles daily. Of course, the number of feet of fall is many times greater at Niagara than it would be at the proposed dam, but even so the total horse power available at the dam would be more than fifty times that of the whole of the Niagara Falls.

The site of the proposed undertaking is between the headlands of Antrim and Cantire. On both sides the ground is described as high, and on the Irish side there rise several peaks of considerable height, viz., from nine to twelve hundred feet. These are sufficiently near the shore to be used to dig materials from to be gravitated down to the dam, and the fact is of great importance in connection with reducing the expense of the work by doing away with the necessity for power for the traction of these materials.

The channel is, as has been said, some fifteen miles in width and of varying depth. The average depth is about three hundred feet, and the maximum is given by Mr. Lodian, in the Electrical Engineer of January 34th last, as four hundred and seventy-four feet; in many places it is as little as two hundred. The bottom is described as of "shells, stones, and rock," which would probably hardly settle at all under the weight of the dam. The current is six or eight miles an hour, varying somewhat at different points in the cross-section of the channel. The total quantity of material necessary to form the dam or isthmus would be in the neighborhood of five hundred million cubic yards. One can imagine that