Physical principle surveys by Cleaver and Weyl stated the antigravity research was not based on any recognized theoretical breakthroughs. Cleaver's skepticism suggested an alternative rationale for establishing that research was based on a science fiction novel. Weyl charged publishers with poor journalism; attacked their terminology; and gave the highest rating for prospective physical principles for gravity control propulsion to Burkhard Heim's works. Stambler leveled harsh criticisms against Gluraheff's gravitation hypothesis. Talbert and other authors listed the following three agencies as the principal facilities that had conducted the theoretical research: