Popular Science Monthly/Volume 45/August 1894/A Proposition for an Artificial Isthmus
|A PROPOSITION FOR AN ARTIFICIAL ISTHMUS.|
A STUPENDOUS scheme has recently been seriously suggested for the utilization in British waters of the energy of ocean currents for the purpose of distribution of power and light by means of electricity to centers of population at distances up to hundreds of miles from the source. This is nothing less than the proposition to dam the Irish Channel at the Mull of Cantire, where the distance between the Scotch and Irish shores is only fifteen miles, and where the energy of the current from the north is, so far as human requirements go, infinite—that is, would have to be expressed in scores of millions of horse power.
That this proposition is being regarded with some degree of seriousness may be gathered from the fact that a series of hydrographic surveys of the bottom of the channel has been made and charts prepared of the coasts and of the highlands on both sides from which materials might be conveniently got for building the dam. The report of an engineer detailed for the purpose is to the effect that there are no engineering difficulties in the way; by which is meant that, given the means to proceed, it is a possible thing to do, and is, compared, for instance, with the erection of the Brooklyn Bridge, a piece of work requiring merely enough brute force.
The idea is not primarily to afford a land junction for purposes of easier communication—although, of course, if the dam were constructed, a railway would be laid across—but, as mentioned, to give 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 this amount of material removed from the crowns of a few high hills in the vicinity would alter the landscape considerably, and that this alteration, together with the turning of the Irish Sea into a landlocked bay, might confuse a person acquainted with the locality only as it had been before the commencement of the work. The territory to be acquired for the land work would not be expensive, as the country on both sides is almost desert.
It is proposed to construct two generating plants near the two shores respectively, each to be used to supply the country to which it is nearest. In order not to interfere with navigation, it is suggested to enlarge the canal of Crinan and to make a cut through the isthmus of Tarbert. To the writer it does not seem that these means would be better than simply to cut through the dam and provide suitable locking facilities.
One of the remarkable results which, it has been pointed out, would flow from the construction of such an artificial isthmus is the lowering of the level of the Irish Sea along the east coast of Ireland, and thus rendering the marsh lands in that section capable of receiving a high degree of cultivation.
Besides the great interest that any such plan must have in itself, from the fact of the important change in the geography of the British Isles which it would bring about, the results that would flow from a utilization of a part of the tidal power for distribution throughout the kingdom are most impressive. Our means for the distribution of power electrically have developed, within the past year or two even, to an extraordinary degree. Two years ago it was possible to transmit electricity for lighting purposes a great number of miles from the point of generation, but it was not commercially possible so to distribute electricity for power purposes. The reason for this is that in order to have electricity in a safe form for use in houses, mills, or car lines it must be supplied at low voltage (or electrical pressure); on the other hand, if we are not to use an utterly prohibitive weight of copper conducting wire we must transmit at high voltage. What is done, therefore, is to transmit at, say, ten thousand volts and transform at the consuming end down to anywhere from five hundred to one hundred volts; the trouble is that there is no practical way of transforming direct currents, and until recently the alternating could not be used to work commercial motors. Now, however, due largely to the work of Mr. Nikola Tesla, we have motors that operate at very good efficiency on alternating circuits. The methods of insulation and of polyphase transmission have, moreover, been improved greatly within a year or two, and these have brought up the capabilities of the wire both for carrying more current and working at higher voltage than was before the case. In the present state of the art it would be safe for an electrical engineer to contract to transmit any amount of power one hundred and fifty miles with a total loss on the line, due to fall of voltage, or "drop," and leakage, of not more than twenty-five per cent, and this without being too extravagant of copper. The voltage on such a line would be, however, much more than that referred to above—probably twenty-five thousand volts.
The distance from the Scotch side of the proposed line to London by air line is three hundred and sixty-five miles, and it is only reasonable to expect that the first decade of the twentieth century will see things so perfected as to admit of transmission over this distance of any desired amount of power. As it is, the great power-consuming counties of York and Lancashire, particularly the former, would to-day be accessible from the proposed power generators.
If we glance at the ultimate results of all this, we shall see them to be enormously far reaching. The limit to Britain's commercial greatness may be set, as things are now, at the giving out of her coal mines. These are not by any means inexhaustible, and the drain upon them is something awful. The amount used in generating power alone is annually in the scores of millions of tons, and this is over and above what is used for house-heating, cooking, etc.
Suppose now that there comes from the north an inexhaustible supply of electric energy—inexhaustible, that is, as regards the driving power it draws on, and limited in practice only by whether one is willing to pay the moderate price that its generation, transmission, transformation, etc., cost—we should have here a solution of the whole question of the future of the coal fields. The electrical power would be sufficiently cheap for general use, and in the great textile manufacturing districts the hum of the hundreds of thousands of cotton and woolen spindles would be supplemented by the lower note of the driving motors. Electric heating for culinary purposes is pre-eminently satisfactory, not only for its cheapness, since one can use the heat just where it is needed and avoid the waste of ninety-five per cent of the heat employed due to hot air going up the chimney of a cooking range and to radiation to an already overhot kitchen, but also on account of its entire cleanliness and reliability. If the price of coal should go up at all seriously, due to prolonged strikes, or to other causes, it would pay to use electricity for even house and store heating. In the vast iron-smelting industry it could be applied to at least greatly reduce the amount of fuel at present used. The only important place where it could not certainly pretty well displace coal would be in seagoing vessels, for they can not now, and probably never will be able to, navigate the ocean on the trolley principle, and it has to be said that it looks more like the job of a century than of a decade to get the storage battery in shape for transatlantic working.
But the railways would all be run by it, and arc and incandescent lamps would shine on the country roads and in rural hamlets all along the distributing lines in the kingdom. The reign of electricity would have set in, for Great Britain at least, in a sense not realized at all as yet, though we speak of the present as the age of electricity; and the deadly smoke from London, Manchester, and Liverpool chimneys would cease, with its accompanying black and yellow fogs and consequent stagnation of business and various kinds of illness. St. Paul's could be cleaned up once for all and shine forth in its whiteness for generations, instead of becoming again the grimy and disreputable-looking object that the soot from London's bituminous coal has made it.
It is hardly to be expected that the great work referred to will actually be begun just yet, although it would be little more than an even thing between the cost of this fifteen-mile dam and Manchester's thirty-five-mile ship canal, but it is one of the great projects that the near future is likely to have in store, and all the results I have foreshadowed are logical outcomes of it. The length of time that the construction of such a work would require has been estimated at in the vicinity of three years, if properly pushed, and the cost would probably be something over one hundred million dollars.
Considering the thing from the broad standpoint of the change in the whole geography of the British Isles which would follow the construction of the isthmus, several most interesting and extremely important questions arise. As to whether these have been all carefully investigated by the projectors of the proposed enterprise I am not aware. In the first place, what would become of the water which at present finds a vent through the Irish Channel in case this channel were stopped? It would presumably go by the west coast of Ireland and a small part, perhaps, up round by the north and east of Scotland; and the question is, would this have a salutary effect upon the west Irish coast, and would it withdraw a part of the Gulf Stream's benign influence from England and the east coast of Ireland? The result of the work might possibly show it to have been unwise to tamper with the natural course of a main branch of that ocean current which is known to have such an excellent influence on the climate and temperature of the British Isles, which, as everybody knows, are as far north as Labrador. The possibility reminds one of the story of the Anglophobiac American who proposed cutting a canal through Yucatan, or some such locality, in order that the Gulf Stream might be nipped in the bud, so to speak, and never reach England at all—thus turning, as he expected, that island into an abode of arctic snow and ice.
Another feature of the case is the fact that the daily tides would not be the same on the two sides of the dam. To the north one could look clear out to sea over the Atlantic Ocean; to the south is about three hundred miles of practically inland water before one gets out to the open ocean coast. The tides on the open coast are about the same height and come at about the same times south and north; and at present, at any given point in the Irish. Sea, the height of the sea level at any time is determined by the resultant of the tides from the north and south respectively. The construction of a dam at the northern entrance would leave the whole Irish Sea subject only to the influence of the tides from the south, while on the north side of the dam the tide level would be the same as that of other points on the open coast. Since, now, it would take some time, probably several hours, for the effect of the southern tide to reach the south side of the dam, the tides on the two sides would be anything but synchronous. When the tide Was at its height at the north side it would be, perhaps, half-way up on the south, and would be high on the south by the time a considerable recession had taken place on the north. This variation would have a most important bearing on the working of the power machinery at the dam, because, instead of the difference of level between the water on the two sides being constant, and giving therefore a constant pressure, it would vary so as to be at times greater and at times less than would be the case if the effect alluded to did not take place. In order, therefore, to supply an equable driving head to the dynamos, the turbine wheels would have to be powerful enough to work up to the required capacity on the minimum difference of level. Since the power made available by the dam would be remarkable for the vast volume of water to be drawn on, rather than for great difference of level, the interference of the tides in at times reducing this difference perhaps considerably would be a matter of grave inconvenience in the way of the successful operating of the power generators.