With the increasing need for storage of granular materials a proper approach to the design of silos has become more important than ever. Rigorous methods of design have been hindered by the incomplete knowledge of force actions within the silo during no flow and discharge conditions. Conflicting reports have been quoted in the past as to the difference in conditions set up in the silo during discharge with the result that at the present moment it is still not quite clear whether any provision should be made for dynamic effects produced during discharge. To clarify this situation the author undertook an investigation on a model silo, with sand as the fill material, in which the flow characteristics, the rate of discharge, the pressure distribution on the base and the total load carried by the base and walls, at rest and during flow, have been investigated. The results of this investigation are presented and compared with some of the better-known theories on silos. A new theory is also put forward to account for differences in conditions observed during discharge.