Bibliographic information from the title page of the book (mine is a signed copy by Boulton):

Second Edition.
SONGS OF THE FOUR NATIONS.
A Collection of Old Songs of the People of England, Scotland, Ireland and Wales, For the most part never before published with complete Words and Accompaniments.
Edited by HAROLD BOULTON,
With Traditional Words or Original Poems and Translations by Nicholas Bennet, Harold Boulton, Rev. Owen Davies (Eos Llechyd), F.A. Fahy, A.P. Graves, Dr. Douglas Hyde and G.M. Probert.
The Music Arranged by ARTHUR SOMERVELL.
J.B. Cramer & Co., 201, Regent Street, London.
mdcccxcii.

Boulton says in the Preface: "Dr. Douglas Hyde is also to be heartily thanked for his poems in the ancient Irish tongue." (p. viii)

~Masato