1. For the accelerating tubes of the multi-stage lens system, see, for example,E. B. Bas, L. Preuss, andW. Schneider, ZAMP10, 533 (1959)G. Henneberke, Nucl. Instr. & Meth.7, 89 (1960).
2. M. Morikawa, J. appl. Phys. (to be published).
3. K. R. Spangenberg,Vacuum Tubes (McGraw-Hill Book Company, Inc., New York 1948).
4. M. Bernard etP. Grivet, C. R. Acad. Sci. Paris233, 788 (1951);M. Bernard etP. Grivet, Ann. Radio Electr.7, 3 (1952).
5. For the detail of the manipulation to derive the formulae of the cardinal elements of this lens system for the limiting case of α=0, see the work cited in footnote 3.