158 ON SURFACE WAVES PRODUCED BY SLEDGES. 



(probably as the square of the velocity). Hence the effect of 

 slow heavy traffic and of light rapid traffic respectively will be 

 different in respect to the production of ruts and of transverse 

 inequalities respectively, the latter being produced chiefly by 

 rapid driving.* 



While these matters deserve our passing attention, it must be 

 well understood that wheeled traffic does not produce large and 

 regular undulations like those formed by sledges. 



A slight transverse undulation in foot-paths, such as the Broad 

 Walk in Kensington Gardens, has not necessarily any connection, 

 except that of form, with waves. Such paths, being highest in 

 the centre, rain runs off transversely to their length, making 

 transverse grooves, towards which the water drains off from 

 both front and rear. The places first lowered are thus kept 

 damper, and therefore softer, than the intervening spaces, so 

 that the hollows wear away more readily than the convexities, 

 and the tendency is for the path to acquire a slightly undulating 

 longitudinal section. 



* It is permissible to speculate upon a connection between this passage from 

 smooth -running to jolting- running and the transition from smooth, steady flow 

 of slow-running water to sinuous or eddying flow in swift-running water, 



