Letters of Junius. In 1871 was published a book entitled The
Handwriting of Junius Professionally Investigated by Mr. Charles
Chabot, expert. The object of this book is to prove that Sir Philip
Francis was the author of these letters. On the 22nd May, 1871,
appeared an article in the Times to show that the case is “not
proven” by Mr. Chabot. Mr. Pitt told Lord Aberdeen that he knew who
wrote the Junius Letters, and that it was not Francis. Lady Grenville
sent a letter to the editor of Diaries of a Lady of Quality to
the same effect.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894