The two volumes published by him in the fifties both represent a treasure trove of analysed data.
In the first:
A Grammar of Manichaean Sogdian, Oxfored, 1954.
Although it was the result of a long work already presented nine years earlier as a Ph.D. thesis, he follows Henning’s teachings in examining the structure of the Manichaean Sogdian language on the basis of fragmentary manuscript material in a way that still stands as an epitome of systematic and complete treatment.
In the second:
The Avestan Hymn to Mithra, Cambridge, 1959.
He introduces a new era in Avestan scholarship.
Leaving aside his contributions to Sogdian and Avestan Studies, the articles on the Bactrian inscription of Surkh kotal, his studies on the reconstruction of Iranian words in the Elamite tablets of Persepolis and on what he called the “alloglottography” of Old Persian remain examples of philological research.