Experiment is the sole source of truth. It alone can teach us something new; it alone can give us certainty. ... [p. 144] But every experiment is long and difficult, and the labourers are few, and the number of facts which we require to predict is enormous; and besides this mass, the number of direct verifications that we can make will never be more than a negligible quantity. Of this little that we can directly attain we must choose the best. ... [p. 145] This is the role of mathematical physics. It must direct generalisation, so as to increase what I called just now the output of science.
Published before 1923