Patents, which grant intellectual property rights to inventors, are rich sources of technical and research data.
Much of this data is never published or disclosed anywhere else.
Image: O. H. 8 W. M. Jewell, Inventors. Chemical Feeder. 1889. Google Patents.
There are four types of patents:
"Utility Patents may be granted to anyone who invents or discovers any new and useful process, machine, article of manufacture, or compositions of matters, or any new useful improvement thereof;
Design Patents may be granted to anyone who invents a new, original, and ornamental design for an article of manufacture;
Plant Patents may be granted to anyone who invents or discovers and asexually reproduces any distinct and new variety of plants" Source: US Patent and Trademark Office;
Reissue Patents are granted if there is a substantial error or errors in the original patent.