FLANGES OF AUSTRALITES (TEKTITES) 19 
Velocity of flight probably controlled the limiting height of 
flow ridges on forward surfaces; in the final phase of flight, 
these heights were at a maximum of 1 mm., and the distances 
between the ridges reached a maximum of 3 mm. to 4 mm. nearest 
the front pole. , 
Only translatory motion is here considered, since rotary move- 
ments must greatly complicate motions in the boundary layers of 
air and their effects. 
At supersonic speeds, if the motion of the solid is purely 
translatory, a disturbance of a permanent type would he set up 
in the shock waves of air ahead of the australites. Such shock 
waves are considered as sheets in which there is discontinuity of 
velocity and they travel in front of the body producing them at 
the same speed and in the same direction as that body (Durand, 
1935). At all other points the shock waves move obliquely to the 
direction of flight (cf. bullet in motion, illustrated by Durand, 
1935). Wavelets are formed in the air layer in contact with the 
australite wherever there are irregularities (e.g., flow ridges 
perhaps) upon the curved forward surface. Pressure increases 
in such regions during separation of the main air-stream from 
boundary layers, i.e., between points of origin of the shock 
wavelets, causing within these areas differential dragging of 
small amounts of plastic glass with the result that flow lines are 
truncated in the flow troughs. 
Reverse and secondary reverse flows in the boundary layers of 
air caused whirlpools or vortices about the equatorial regions, 
where the main flow of air diverged from the bodies. These 
vortices generated stresses that caused complex puckering of 
surface structures in thin films of plastic glass. The stretching, 
bending and twisting of glassy particles in the flanges resulted 
from (a) turbulency in the plastic glass moving back under 
pressure to form the flange and (b) jamming during the develop- 
ment of the flow structures in the glass. 
The total drag on forward surfaces is set up both by pressure 
and by friction ; these are functions of the shape and surface 
areas of the bodies. Conversion of mechanical energy into heat 
is due to the viscosity and conductivity of the air; viscosity and 
conductivity are also regarded as maintaining shock waves of a 
permanent type (Durand, 1935). The concentric flow ridges on 
forward surfaces of certain australites are in keeping with such 
shock waves and wavelets; and since these can be caused only 
by non-rotating bodies, the inference is that australites with 
concentric flow ridges did not rotate during flight through the 
atmosphere. 
