A method of investigation which may be appropriately called the "synthetic method" is proposed ; in this method the behaviour of the valence electron in a metal is not assumed from the starting of investigation, as usually done in the prevailing theory of metals ; but, from X-ray spectrum, the energy level or levels which are expected to be associated by the valence electron, are determined. For Cu, it was taken as that, X-ray L-satellites, Lβ\u27, λ 12.989, β\u27\u27\u27 12.911 ; α\u27\u27 13.233, α\u27\u27\u27\u27 13.176A, [E. Gwinner, Zeits. Phys. 108 (1938), 523], are due to the transitions. L_-E_1, L_-E_3 ; L_-E_2, L_-E_4, respectively, E_1～E_4 being the energy levels associated by the valence electron ; next, they were combined with K_ and K_, respectively, and obtained the distances from K ; finally the relative positions of E_1～E_4 were computed for comparison with the other phenomena which are expected as due to the behaviour of the same electron as above concerned, this comparison being done in the next paper
