Viscous Instability of an Incompressible Full Jet

The instability with respect to infinitesimal, antisymmetrical disturbances of a viscous, laminar, plane jet is investigated for an incompressible fluid. The minimum critical Reynolds number is found to be 4.03 when the unperturbed flow is assumed to be parallel and 12.4 when some corrections for nonparallelism are made. In the actual jet flow it does not appear that a small two‐dimensional disturbance in itself leads to transition, because as it propagates downstream the disturbance leaves the unstable region in the $\mathrm{\alpha ‐R}$ plane, and then proceeds to damp out.