A theory of the current distribution in triodes with positive grid is developed on the assumption that space charge and the initial velocities of both primary and secondary electrons may be neglected. This theory, which is originally due to De Lussanct de la Sablonière, has been put in a more lucid form; and a graphical method has been developed to check the applicability of this theory to any set of observations. From the graphs used for this purpose the different distribution functions which enter the equations can be read off in a very simple manner. In some cases theory and experiment are in excellent agreement; discrepancies occurring in other cases are discussed. In connection with these observations the basic assumptions underlying the theory are subjected to a closer scrutiny.