The principal physical constants are calculated by the theory developed in Relativity Theory of Protons and Electrons and subsequent papers, and are compared with the values given by Birge (1942) in Reports on Progress in Physics, 8. There is satisfactory agreement with Birge's values as they stand. But the theory also indicates that small corrections are required in the computation of certain constants from experimental data; when these corrections are included, the small discordance between the spectroscopic and deflection values of e/m_ec disappears, and the agreement of observation and theory is complete. It is concluded that there ought to be no difference between the direct and indirect values of h/e. The calculated constant of gravitation is 6.6665.10^-8; and it is pointed out that the expected agreement of the calculated and observed values is not affected by the mean chemical constitution of the universe or the free radiant energy in space - a point previously left doubtful. As the purpose is not to justify or explain the theory but to compare it with observation, theoretical explanation is limited to the points which arise in adapting the theory to practical comparisons.