Mr Matheson on a new mode of constructing Harbours. 85 



through which opening the receding tide, assisted by the land 

 stream, passed into the harbour, and swept round and again 

 passed out at its mouth. By this action of the tide, the har- 

 bour was kept perfectly free from any tendency to sand up ; but 

 in the course of a very short period, after the works were finish- 

 ed, and this opening closed up, in completing the harbour, the 

 sand accumulated in it to such a degree as to make it inac- 

 cessible to vessels of even very small tonnage, and to cause the 

 outlay of a large sum of money in the erection of an outer harbour 

 which it is probable will be visited with the like obstructions, if 

 they have not already taken place. 



The practical hint thus afforded induced the writer to form 

 the idea of erecting the necessary works for sea harbours, with 

 artificial openings, so constructed as to enable the waters still to 

 retain their natural motion, and by that means to avoid eddies 

 and stagnation, by the latter of which the sand and alluvion are 

 deposited, and by the former of which the deposition is shift- 

 ed and whirled from place to place. 



His plan, therefore, may be very shortly described. Where- 

 ever it may be necessary to erect a harbour, or to extend the 

 works of one in a situation where sand or alluvion may be likely 

 to accumulate, he proposes, after laying a solid foundation of 

 stone, to make the next range of building consist of a succession 

 of arches of such a height of opening as not to disturb any class 

 of vessels that may frequent the harbour, while they are pro- 

 tected and sheltered by the solid building erected over these 

 arches, and at the same time the openings shall be so proportion- 

 ed to the depth of water, at the different points of the building, 

 as to allow the tide to pass freely through. 



To enter into any detail as to the particular mode of con- 

 structing the works or of forming the arches, &c. is quite un- 

 necessary here, as these must vary according to circumstances. 

 It is enough, if it is admitted that walls with arches may be 

 constructed under water, as well as solid walls ; because so much 

 being granted, it will appear sufficientlyobvious that the motion 

 of the tide, cither in approaching or receding, will naturally pass 

 through these arches, and carry with it both in advancing and re- 

 tiring, whatever is mechanically united with it, and the agitation 



