That the second mode of reading the line in question is the proper one, may be shown by reference to the stanza wherein it occurs.
Let Érin remémber her dáys of óld,
Ere her faíthless sóns betráy'd her,
When Málachi wóre the cóllar of góld,
Which he wón from the próud inváder.
Again, such a line as
For the glory I have lost,
although it may be read
For the glóry I have lóst,
would be read improperly. The stanza wherein it occurs is essentially dissyllabic (a x).