The phenomenon of nonisotropic propagation consists in the spontaneous development of blisters or cells
on the surface of a combustion wave. The present experiments on spherical flames and the experiments
of Markstein on flames in wide tubes show that the phenomenon is characteristic of nonstoichiometric explosive
mixtures in which the deficient reactant constituent is also the constituent of largest diffusivity. This
su~gests that the p~enomenon is primarily caused by the effect of diffusion processes on the burning velocity.
It IS proposed that III curved areas of the wave that are convex with respect to the burned gas, the burning
velocity is reduced because the lines of diffusion diverge, and hence the concentration of the faster diffusing
constituent decreases; whereas in concave areas the lines of diffusion converge, and hence the concentration
of the faster diffusing constituent increases. In rich mixtures of hydrocarbon and oxygen, additional evidence
for the effect is furnished by the emergence of carbon streamers and by characteristic changes of light emission
from convex wave areas, showing that the oxygen concentration, and probably therefore the burning
velocity, is decreased in these areas below the average for the mixture.