494 POPULAR LECTURES AND ADDRESSES. 



shows very curious phenomena regarding the 

 resistance at different speeds. As the speed is 

 raised, the resistance increases; but on a further 

 increase of speed, it seems as if it was beginning 

 to diminish ; the resistance never quite diminishes 

 however with increase of speed, but only increases 

 much less rapidly. The curve indicating the 

 relation of the speed to the velocity has a succes- 

 sion of humps or rises, each showing a rapid 

 increase of resistance ; between these it becomes 

 almost flat, showing scarcely any increased resist- 

 ance. Froude has explained that thoroughly by 

 the application of this doctrine of ship waves which 

 I have endeavoured to put before you. When the 

 effect of the entrance or bow, and the effect of the 

 run or stern, are such as to annul or partially to 

 annul each other's influence in the production of 

 waves, then we have a favourable speed for that 

 particular size and shape of ship. On the other 

 hand, when the crest of a wave astern due to the 

 action of the bow agrees with the crest of a wave 

 astern due to that of the stern, then we have an 

 unfavourable speed for that particular size of ship. 



