Gods of the Jungle by Nelson S. Bond

So they dropped the matter there, completely unable to solve the problem, each convinced that his theory was correct, none without a lingering doubt but that the other's might be true. And the days sped by.

They were fruitful days. Lake, who had a flair for the philological, spent much time studying the Gaanelian language. To Red and Ramey, as professional airmen, what was of particular interest was the matter of spaceflight. Gaanelian ships, Sugriva told them, called regularly at every inferior conjunction of Earth and Venus, Videlian craft less frequently. "But often enough," the blue lord admitted ruefully.