transition by several means. Since the turbu- 
lent boundary layer transfers heat more easily 
than the laminar layer, frost, water, and oil 
films will be removed more rapidly from the 
area aft of the transition point. Also, a-small 
probe may be attached to a stethoscope and 
positioned at various points along a surface. 
When the probe is in the laminar area, a low 
“hiss” will be heard; when the probe is in