In this paper a law of primary-current division between a positive grid and plate which is believed to be more accurate than those previously presented is deduced from a study of the electron paths within the tube. It is found that the ratio of plate to grid current may be expressed in the form ip/ig= (L + Mep/eg)/(P —Qep/ eg): When plotted on logarithmic paper against ep/egthe curve of the ratio ip/ighas a slope varying between ¼ and ¾ and assuming the slope of ½ over a considerable range. This provides a theoretical justification for the previously observed form, (ip/ig) = δ(ep/eg).½The effective grid area for the condition of equal positive grid and plate voltages is found to vary between 120 and 180 per cent of the actual grid area for ordinary triodes. The effective grid area in terms of the electrode dimensions is conveniently expressed by means of a nomograph as is also the current-division factor. By means of these nomographs the essential factors related to positive grid currents may be rapidly determined for any tube. An excellent check between the predicted and measured currentdivision law was obtained. Measured and observed values checked within two or three per cent for all factors.