Expressions are obtained in closed form for the transient stress in a homogeneous isotropic elastic half-space whose surface is subjected to a constant uniform pressure over a circle whose radius increases in proportion to the square root of time. The positions of the wave fronts are derived, together with the magnitudes of the discontinuities of the stress components across them. It is shown that a Rayleigh surface wave appears at the moment when the radius of the area under load is increasing with the Rayleigh wave-speed. The behaviour of the stress and strain is described in the region of the stress singularity at its leading edge.