CONTENTS. xi 



SECTION IV. CEMENTS. 



PAGl 



Portland cement Analyses of clay and chalk Process of making Portland 

 cement Air-slaking Porosity in concrete Indications of good Portland 

 cement Bate at which Portland-cement briquettes gain strength with 

 age Apparent decrease of strength at age of seven or eight months 

 Analysis of good Portland cement Roman cement Medina cement . 124 



SECTION V. TIMBER. 



Various kinds of timber used in sea-works Destruction of timber by sea- 

 worms, etc. Teredo navalis Limnoria terebrans Ghelura terebrans 

 Methods of preserving timber Greenheart, sneezewood, and jarrah repel 

 sea- worms Creosoted Baltic red- wood, oak, and teak useful in some 

 localities Pitch pine quickly attacked by sea-worms Greenheart and 

 jarrah liable to split American rock elm useful for fendering Black 

 ironwood eaten freely by Teredo navalis , 131 



SECTION VI. IKON AND STEEL. 



Durability in sea-water Records differ widely Results of experiments- 

 Effect of galvanic action Structural and chemical differences affect rate 

 of corrosion Simple corrosion Rate of corrosion of plates, etc., of s.s. 

 Gambia Effect of exposure on castings at Bell Rock lighthouse, on 

 wrought-iron rails at Port Elizabeth, on ironwork of piers at Ramsey and 

 Port Elizabeth, and on ironwork of beacon at Wolf Rock Beardmore on 

 decay of iron Wrought iron more durable than cast iron in sea- water 

 Mallet on preservation of iron Redman on decay of iron Pier at Milton- 

 on-Thames Gravesend town pier 138 



CHAPTER VIII. 



CONSIDERATIONS AFFECTING THE GENERAL DESIGN OF HARBOURS. 



No general rules for designing harbours can be laid down Preliminary 

 investigation Survey Materials available for works Quarry and work- 

 yard sites Transport of materials Description of vessels to be provided 

 for Beaching ground Spending-beaches Future development of port 

 Degree of shelter required Anchorage Good and bad holding-ground 

 General requirements of harbours of refuge Natural features of sites 

 should be utilized 146 



CHAPTER IX. 



ESTUARY HARBOURS GROUND PLANS OF HARBOURS ENTRANCES. 



Estuary harbours " Bars "Lagoons Removal of "bars" Concentration 

 of ebb current Importance of large tidal compartment Protection of 

 ebb current Site of entrance Maintenance of depth Relative value of 

 upland and tidal waters Borings on site of proposed entrance, etc. 

 Physical and nautical requirements often opposed to each other at 

 harbour entrances Ground plans of harbours Wave expansion 

 Direction of main entrance Parallel jetties Isolated breakwaters 

 Harbours with two entrances Roadsteads Advantages of deep water at 

 entrance Strong current across harbour entrance objectionable Widths 

 of entrances Reduction of waves Relative advantages of embayed and 

 salient sites for harbours 150 



