92 IMPRO VED FISHER Y HARBOUR A CCOMMODA TION 



As an adjunct in the shape of ladders and ringbolts, and 

 chains, or as stiffeners to a wooden pier, this material will 

 probably always remain in use. Twenty-five experiments 

 at the Bell Rock, in different kinds and combinations, when 

 ungalvanised, oxidised with much the same readiness. The 

 zinc stood 3 or 4 years, after which the iron thus coated 

 oxidised, as the ungalvanised iron. Castings one inch 

 square perished at the rate of one inch to the century. 

 An apparently sound bar was reduced in strength from 

 4068 Ibs. to 2352 Ibs., having lost nearly half its strength 

 in about fifty years. 



Mr. Stevenson, after adducing a number of instances of 

 the perishable nature of iron, sums up as follows 



Where there is room for choice, neither cast nor malleable 

 iron should be used as a principal constituent of sea-works, 

 which are to be so deeply submerged as to become difficult 

 of inspection and repair. 



When we find that even thick pieces of cast iron, and 

 those not constantly immersed, decay so rapidly, what can 

 be expected of the durability of malleable iron bolts and 

 tie-bars which do not exceed an inch or two in diameter ? 

 And what reliance can be placed on the stability of deeply 

 submerged marine structures, the unity of which depends 

 upon such perishable bonds ? 



OF THE DRESSING AND METHOD OF ASSEMBLING 

 MASONRY IN SEA WORKS. 



" The requirements for marine masonry are, in many 

 respects, nearly the opposite for land architecture. What is 

 wanted in sea-work of the ordinary kind, which neither 

 consists of framed carpentry, nor has been rendered mo- 

 nolithic by cement, is that each stone shall gravitate 



