In common with most other Maya scholars, Morley was particularly interested in the mysterious nature of the Maya script. The essentials of the calendric notation and astronomical data had been worked out by the early 20th century, and by the 1930s John E. Teeple had solved (with Morley's encouragement) the glyphs known as the "Supplementary Series", proving that these referred to the lunar cycle and could be used to predict lunar eclipses. However, the bulk of the texts and inscriptions still defied all attempts at decipherment, despite much concerted effort. It was Morley's view, and one that found wide support, that these undeciphered portions would contain only more of the same astronomical, calendric and perhaps religious information, not actual historical data. He wrote in 1940, "time, in its various manifestations, the accurate record of its principal phenomena, constitutes the majority of Maya writing." He also wrote that he doubted that any toponym would be found in the texts. He supposed that the Maya writing system was one based chiefly upon ideographic or pictographic principles, and that if present any elements of phoneticism would always be "overshadow" by the ideographic meaning assigned to each glyph." That is to say, in Morley's view each glyph substantially represented words, ideas and concepts "in toto", and did not separately depict the individual language sounds as spoken by the scribes who had written them (with the possible exception of an occasional rebus-like element, as had already been demonstrated for Aztec writing).