492 POPULAR LECTURES AND ADDRESSES. 



Plates 83 and 84, and as a lesson it conveys more 

 than any words of mine. 



Here is a table (page 491) giving the length of a 

 free wave ; and remember, when once the waves 

 are made and are left by the ship, they are then 

 and thereafter free waves. At 6 knots per hour 

 the wave-length is 19^9 feet ; at 12 knots it is four 

 times as great. At 10 knots it is 54 feet ; at 20 it 

 is four times as much. The greatest speeds in 

 Froude's diagrams give about 240 feet length of 

 wave. Now that is a very critical point with 

 respect to the length of the wave and the speed of 

 the ship. I may tell you that Froude the elder 

 and his son Edmund have made most admirable 

 researches in this subject, and have poured a flood 

 of light on some of the most difficult questions of 

 naval architecture. 



Parallel Middle Body. I should like to say 

 something about the practical question of parallel 

 middle body. When I first remember shipbuilding 

 on the Clyde, and its progress towards its present 

 condition, a very frequent incident was that when 



