An investigation has been made to determine the conditions under which the voltage sustained by a 2‐ft length of ion‐accelerator tube may be made proportional to the length of the tube. It has been found that such linearity may be obtained if the tube is segmented at 4½‐in. intervals by diaphragms which are so arranged that no straight path is possible from one end of the tube to the other. No significant deterioration in performance of the tube was observed when axial holes were made in each diaphragm up to ¾ in. in diameter. The voltage gradient realized on these tests was 60 kv/cm.