A drawing of the Fahy permeameter from the original patent.
Patent US1196223: http://www.google.com/patents/US1196223
fahy_permeameter_drawing_patent.png
You can use this image freely (there is no need to ask for explicit permission), but you must give the following credits:
United States Patent and Trademark Office, Public domain
Copyright law (17 U.S.C. § 105) states that all materials created by the United States government are in the public domain. However, there are restrictions on use. Anyone incorporating a work of the U.S. Government into a copyrighted work should be aware of 17 U.S.C. § 403. This section requires a copyright notice to contain a statement identifying what portions of the work consist of a work of the U.S.Government. Failure to do so could result in loss of copyright protection for the entire work.