Part I contains a discussion of the work on the
interpretation of the Hertzsprung-Russell diagram with
regard to problems of stellar evolution .
Part II describes the three-colour studies of the
southern galactic clusters NGC 2422, NGC 2423, and
NGC 2437. The colour excesses and distances, corrected
for absorption, are: NGC 2422, 0.06 and 480 parsecs;
NGC 2423, 0 and 450 parsecs; NGC 2437, 0.16, 1450