text: to high). 
  The action of the pressure gradient is such 
  that 
  the favorable pressure gradient assists 
  the boundary layer while the adverse pressure 
  gradient impedes the flow of the boundary 
  layer. The effect of an adverse pressure gradi- 
  ent is illustrated by the segment X-Y of figure 
  1.26. A corollary of the skin friction drag is 
  the continual 
  reduction of boundary layer 
  energy as flow continues aft on a surface.*The 
  velocity profiles of the boundary layer are 
  In the 
  shown on segment X-Y of figure 1.26. 
  area of adverse pressure gradient the bound- 
  ary layer flow is impeded and tends to show a 
  reduction in velocity next to the surface. If 
  the boundary layer does not have sufhcient 
  kinetic energy in the presence of the adverse 
  the 
  pressure gradient, 
  lower 
  layer may stagnate prematurely. 
  boundary 
  
  the  levels of 