96 MOVEMENT 



discovered that the various currents reached the obstacle 

 in a more or less oblique direction, and that near the 

 lower edge of the inclined plane the currents divided 

 in conformity with Avanzini's theory. At the back 

 of the obstacle the behaviour of the currents was 

 variable. The velocitv of the molecules in the different 



Fig. 64.— Changes in velocity and. in direction which occur in the liquid molecules of 

 a current which meets an inclined plane. 



parts of the basin must be deduced from the distance 

 which separates any two consecutive images. 



The latter are sometimes fused together in the form 

 of a continuous trajectory, and thus demonstrate the 

 sluggishness of the current. On the other hand, when 

 widely separated, the intervening distances can be 

 measured with a scale. Each interval represents ^ 

 of a second in time, and hence the absolute velocity 



Fig. 65.— Effects produced on a current by the immersion of a solid rectangular box. 



of the stream can be calculated. It is equally easy 

 to determine the behaviour of the currents when they 

 meet obstacles of different shape. For instance, if a 

 rectangular box is placed in the stream (Fig. 65), of the 

 same width as the tank, and provided with a glass top 

 and bottom, the currents which meet it become deflected 

 from their course, and pass with increasing rapidity 



