Geometry and Empirical Science (article)
(engl.)
at Digital Text International
[www.ditext.com/hempel/geo-frame.html]

On the Nature of Mathematical Truth (article)
(engl.)
at Digital Text International
[www.ditext.com/hempel/math-frame.html]

Problems and Changes in the Empiricist Criterion of Meaning (article)
(engl.)
at Tilburg University
[www.tilburguniversity.edu/research/institutes-and-research-groups/tilps/EPS/Lutz_Hempel.pdf]