ON SHIP WAVES. 471 



Edinburgh and Glasgow on the Forth and Clyde 

 Canal, at speeds of from eight to thirteen miles an 

 hour, each boat drawn by a horse or pair of horses 

 galloping along the bank. The method originated 

 from the accident of a spirited horse, whose duty it 

 was to drag the boat along at a slow walking 

 speed, taking fright and running off, drawing the 

 boat after him ; and it was discovered that, when 

 the speed exceeded the velocity acquired by a 

 body falling through a height equal to half the 

 depth of the canal (and the horse certainly found 

 this), the resistance was less than at lower speeds. 

 Scott Russell's description of how Mr. Houston 

 took advantage for his Company of the horse's 

 discovery is so interesting that I quote it in 

 extenso : 



" Canal navigation furnishes at once the most 

 interesting ^illustrations of the interference of the 

 wave, and most important opportunities for the 

 application of its principles to an improved system 

 of practice. 



"It is to the diminished anterior section of dis- 

 placement, produced by raising a vessel with a 



