SUB AQUATIC ARCHITECTURE. 



217 



SUBAQUATIC MORTAR. PAINT AND VARNISH. 



HAVING now disposed of the chief points in Architecture, 

 we take some of the subsidiary details. 



Of late years, when the traffic between different continents 

 has so largely extended itself, and when shipping has increased 

 both in^the numbers and dimensions of the vessels, it is 

 absolutely necessary that we should have harbours and docks 

 enlarged and multiplied sufficiently to meet the calls upon 

 them. 



Now, it is comparatively easy to construct a building on 

 shore, for all the mortars and cements which are used for the 



TEREBELLA. 



SUBMARINE MORTAR. 



purpose of fastening the stones together are applied when wet, 

 and incorporate themselves with the stones as they dry. But 

 to make a mortar which could be applied while the stones were 

 under water, and would "set" while beneath the surface, was 

 a task not easily to be overcome. Yet it has been done so 

 effectively that at the present day we can build beneath the 

 surface of the water as securely, though not as rapidly, as if the 

 stones had been laid on dry ground. 



Several such mortars are now known, and, as is so often the 

 case with human inventions, have been anticipated in Nature. 



"We have already seen how the Caddis-worm of the fresh 



