This 1940's science fiction book is about a space station located at the Venus/sun Lagrange point (hence the "equilateral" of the title). The station's main mission is to facilitate communication between Earth, Mars and Venus. The crew deals with various crisis (pirates, politics, and dishonest salespeople) and produce some inventions, including the invention an FTL drive and a matter transmitter. Written as 13 short stories, they share a single continuity and setting and the book reads like a novel with 13 chapters. The book has aged well, especially considering that it is hard science-fiction, and the writing is excellent.