David Nishimura has turned up an example of one of the earliest American mechanical pencils - earlier even than a Lownds. Henry Withers received a patent for his pen and pencil combination on March 19, 1834 - the fourth patent issued in the United States for a pencil.
David has also run down some of the history concerning the Withers patent pencil. For those who are interested in early American writing instruments, his article is a must-read.
The link to David’s article: http://vintagepensblog.blogspot.com/2017/06/withers-patent-x-patent-discovery.html. He’s allowed me to repost a few of his pictures here: