This paper [Isherwood, 1959] prompts a discussion on the influence of substrata layers on water-table heights in tile-drained land. For steady-state conditions the effect of such layers can easily be determined by means of electric analogue experiments, and there seems to be no reason why the effect for nonsteady-state conditions cannot be inferred from these results. Assurance of this was given by hydraulic experiments in a sand tank in which a drain was installed and on the surface of which rain could be simulated [Collis-George and Youngs, 1958]; the water-table heights observed at the midway position between the drains in nonsteady-state experiments with falling and rising water tables approximated those observed in steady-state conditions for the same drain discharge rate in experiments with different depths of impermeable floor below the drain axis. Hydraulic and electric analogue experiments (loc. cit.) indicated that the effect of an impermeable layer below the drain was negligible for a layer deeper than 0.3 of the half spacing of the drain channels (i.e., 0.15S in Isherwood's notation) below the drain axis. At a depth of 0.25 of the half spacing (or S/8) it was very small. However, the effect of the impermeable layer on the water-table height was shown to be dependent on the value of q/K (the ratio of the mean flux of water cutting the water table at any time to the saturated hydraulic conductivity) increasing with decreasing q/K. q was given by the drain discharge divided by the catchment area of the drain and was found to be equal to the rainfall in the corresponding steady state. The smallest value of q/K investigated was 0.01.