structural fatigue of a long and tempestuous voyage. Vessels have 

 frequently to carry weights far in excess of their own and unequally dis- 

 tributed, so that when a long steamer takes the ground, it involves the 

 risk of impairing the rigidity of the hull and the adjustment of 

 the machinery 



A century ago the area of the Liverpool docks was only about 13 

 acres ; now the docks form an unbroken chain of six miles in length, and 

 the value of the imports and exports for the year 1874 reached the 

 enormous amount of ^667,733,165. At present, extensive works are 

 in progress to meet the requirements of the increasing commerce of the 

 port ; similarly at Hull, Glasgow, Bristol, and other places. 



The wonderful change that has come over the character of our 

 shipping must be considered with reference to the proportions and details 

 of modern docks. In 1860 the number of vessels registered as belonging 

 to the United Kingdom, consisted of 25,663 sailing vessels and 2,000 

 steamers; in 1874, the number of sailing vessels decreased to 21,464, and 

 the number of steamers increased to 4,033 ; or in other words, while the 

 number of sailing vessels had decreased, the number of steamers had 

 doubled ; but instead of the tonnage simply doubling as well, it increased 

 from 454,327 to 1,870,611 tons, thus showing that steamers are now not 

 only twice as numerous, but twice as large as they were fifteen years ago. 

 This increase of tonnage in the modern steamship is not so much due to 

 increased depth or beam, entailing wide and deep entrance locks, as to 

 increased length ; so that instead of providing dock accommodation for 

 the comparatively short bluff vessels of the past, we are now required to 

 afford accommodation generally for steamers long and thin in character, 

 and, in some instances, exceeding 500 feet in length. 



The construction of docks in a tidal harbour is sometimes attended 

 with many difficulties and obstructions. In the majority of cases, the 

 difficulties and delays attending tide-work are overcome by constructing a 

 coffer-dam, so as to exclude the tide from the area of operations ; but, of 

 course, in ports where the existing accommodation is very limited, 

 this preliminary step is impracticable, and in consequence the work 



