A method has been developed for measuring the pressure-time profiles of the stress waves produced in solids by explosives. The system uses the linear variation of resistance with pressure in a manganin wire. Various pressure profiles are presented, illustrating a range of shock phenomena; in particular a two-wave structure has been detected in glass and granite between pressures of 100 and 200 kb. A large rounded pressure wave observed in glass is attributed to the adiabatic compressibility initially increasing with increasing pressure, a variation opposite to that usually found in solids. A simple treatment is given by which the pressure-volume relationship can be found in this region from measurements of the pressure-time profile. The resulting curve for glass is not inconsistent with measurements by conventional methods in the high pressure single shock region.