Starting in 1940, Science Service issued a series of Things of Science kits, each focused on a single topic, such as magnetism, seed germination, static electricity, or mechanical linkages. Sold only by monthly mail-order subscription, these kits consisted of a small blue cardboard box containing basic materials and detailed instructions, usually to be supplemented by commonplace household materials and objects. The wealth of knowledge and entertainment that could be derived from simple and economical materials set a standard which would later be adopted by the pioneering science and technology center, the Exploratorium in San Francisco.