log HARBOUR CONSTRUCTION. 



When water is confined in joints, the force of the wave-stroke 

 is transmitted by it, and made to act over large areas on the 

 same principle as a hydraulic press. 



The failure of many sea-works may be attributed to this 

 cause, blocks of stone or concrete, even on the harbour side of 

 breakwaters, and the stone pitching of their roadways, having 

 been frequently started out of their places by a heavy wave- 

 stroke on the seaward face of the structure. 



Changes of temperature, by causing expansion and con- 

 traction, form and open out joints, and thus assist the waves in 

 their destructive work. 



An experiment, showing how force suddenly applied is 

 conveyed by water, even when unconfined, i.e. having its whole 

 surface free, may be easily made by filling a small ordinary 

 powder-keg with water, and exploding a copper detonating cap 

 such as those used for exploding dynamite in the midst of it. 

 The pressure exerted by the explosion of the cap upon the 

 water is immediately transmitted to the sides of the keg, with 

 the result that the hoops, and sometimes also the staves, are 

 rent. 



Mr. Mallet mentions another instance, somewhat similar to 

 the above, which he thus describes 



"During the progress of the experiments made by the French 

 artillery at Metz to ascertain the penetration of bullets in water, a 

 long rectangular open-topped trough, about 12 inches in width, the 

 same in depth, and say 20 feet long, was formed of wood, one end 

 being of india-rubber clofch. It was filled with water, and a common 

 musket-bullet fired horizontally into the water through the india- 

 rubber end. To the surprise of all, the trough was split to pieces, 

 both the sides and the ends being thrown asunder." 1 



I will cite one other instance illustrative of the manner in 

 which a sudden shock is conveyed by water. 



Some years ago I had occasion to employ dynamite in remov- 

 ing a submerged structure. Charges varying from 16 oz. to 19 

 oz. were used. When these operations were initiated, it was not 

 anticipated that divers, working at a distance of about 500 feet 

 from the site of the firing, would be inconvenienced by it. They 

 were, however, unanimous in stating that the shock of each 



1 Min. Proe. Inst. C.E., vol. xviii. p. 114. 



