Reviewer Alfred Schild said it was an "excellent, clear and concise account" and "provided a sound balance between physical ideas, analytical formulae and space-time geometry".

He was visiting scholar at King's College London for the academic year 1961–1962, at the University La Sapienza in Rome for 1968–1969, In 1969 Springer published the first edition of his Essential Relativity: Special, General, and Cosmological.

The undergraduate textbook was lauded as a "refreshingly modern approach to the critical problem of teaching relativity theory.

"[5] When the second edition appeared in 1977 a reviewer noted its treatment "reminiscent of Mach's celebrated examination of the foundations of classical mechanics".

On the other hand, the second edition "gives the barest hints of new developments" (models of neutron stars, in X-ray astronomy, supernova explosions, and quasars).

He was impressed with the "discussion of the internal structure of black holes analyzed first in Schwarzschild coordinates, and then in a masterful treatment of the Kruskal extension.