For 90 years, ranging from 1790 to 1880, the government required every patent application to be accompanied by a working scale model of the invention, which could be no larger than 12 inches on each side. This practice terminated after the Patent Office ran out of space to store all of the models. The Rothschild Petersen Patent Model museum in New York maintains the largest private collection of patent models, housing over 4,000. Currently, applicants are neither required nor generally permitted to submit any type of working model unless the Patent Office deems it necessary for proper examination. Once returned to the applicant, the model or exhibit must be retained for the enforceable life of any patent resulting from the application.