They're 15, according to the book "The Art of writing" by John Jenkins, from the year 1813 (yes, 1813) according to archive.org. Although In the book there's a

They're 15, according to the book "The Art of writing" by John Jenkins, from the year 1813 (yes, 1813) according to archive.org. Although In the book there's a text saying it's printed 1818. In the book he lists 15 groups of them and shows two examples for each. https://archive.org/details/JenkinsArtOfWriting/page/n25/mode/2up https://archive.org/details/JenkinsArtOfWriting/page/n25/mod... (page 26 in the built in browser, plate 33 in the book)