Art. XVII. — On the Extinction of Waves at the 

 Entrance of Harbours. 



By Edward Davy, L.S.A., M.K.C.S. 



[Read 11th December, 1884.] 



To prevent the access of a heavy sea into a shipping harbour 

 has always been a desideratum. This object can be accom- 

 plished by means of what is called a breakwater — 

 namely, a strong stone wall, built up from the bottom of 

 the sea ; and what has been called a floating breakwater, as 

 a cheap substitute, is probably a fallacy. 



If a principle can be pointed out by which, at an 

 enormously smaller expense, the same object can be even 

 partially obtained, there is no doubt a benefit would be 

 conferred on the world. I therefore offer the following in 

 the hope that others capable of reasoning correctly on the 

 matter will take the subject up. 



The contrivance which I propose, and which, provisionally, 

 I will call a Wave Extinguisher, consists of three parts — 

 First, a float. 

 Second, a moorage. 

 Third, a tether. 



I shall describe the contrivance as a unit, on the under- 

 standing that any number of them may be required for use. 



First, the Float. — The float may be a log of light wood, or 

 hollow barrel of air, made of whatever material will suit. 



The Moorage may be a basket of durable wood at the 

 bottom of the sea, sufficiently loaded with stones (with the 

 aid of the tether) to prevent the float from rising with the 

 waves. 



The Tether will be a rope or chain of thelength toberequired, 

 according to circumstances. Now, it will appear that on 

 the approach of a wave the float, being so confined, will be 

 unable to rise with or to the top of it, and will consequently 

 be submerged in it; in so doing, it becomes, for the time 

 being, a part and parcel of that wave — displacing water 

 which thus takes its place in the trough between the waves. 

 As the wave passes on it is, of course, lessened by a bulk 

 equal to that of the float it has left behind it. 



