from Edward Bunting, The Ancient Music of Ireland (Dublin 1840), page 22: The strings of the harp.
Irish téad leagaidh
spoken by Gráinne Yeats
Scottish Gaelic teud leagaidh spoken by Tony Dillworth
Irish téad leagtha
spoken by Gráinne Yeats
Scottish Gaelic teud leagte spoken by Tony Dilworth
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The tuning charts in ms29 as well as the printed chart on p23 of the 1840 book indicate that Tead leagaidh and Tead leagtha are related respectively to the flat key (with f natural, a mixolydian scale on G) and the sharp key (with f sharp, a natural major scale on G). Thus, when the f strings are set to f natural on the rest of the harp, the string below cronan G is also set to F natural. However when the rest of the f strings are turned up to f sharp, the F string below cronan G is turned gown to E.
However the footnote here says that the string is adjusted to either F sharp or F natural ‘as the occasion required’.
Note also that the gamut represented in this chart of terminology is based on the 30 strings of the Downhill harp: C D E G a b c d e f g g a b c' d' e' f' g' a' b' c'' d'' e'' f'' g'' a'' b'' c''' d'''. The tunings in ms29 indicate instruments with two extra strings below this range, and interestingly there appears to be another gap or movable string at BB-C.
See also Alasdair Codona's comments on this string.
Simon Chadwick 2008
Tead leagaidh - Falling string
Tead leagtha - The string fallen
The second of these, reading téad leagtha, causes no difficulty, because téad means 'a string' and leagtha means 'having been dropped', being the past participle of the verb leag, a transitive verb meaning 'knock down, lower or drop' (different from its intransitive parallel tuit, which means 'fall': Bunting's English is a little misleading on this point).
No.22, however, which is called Teadleaguidhe, 'the falling string, or high bass key', in a footnote on on p.23, is more difficult. Its literal meaning may be 'string of dropping', which Bunting understands as equivalent to 'in the process of falling' (but not quite leagtha, 'dropped'). But this meaning is only possible if leagaidh is the genitive case of leagadh, 'dropping', verbal noun of leag. One difficulty with this is that Irish verbal nouns ending in -adh (the most common form) normally have their genitive in -tha; thus the normal genitive of leagadh is leagtha, identical in form and pronunciation with its past participle.
We may therefore question the validity of Bunting's distinction between leagaidh and leagtha here, though the musical distinction is doubtless real enough. One possibility is that we take account of Scottish Gaelic, where the genitive of verbal nouns in -adh is quite correctly -aidh, so that leagaidh therefore could mean 'of dropping', allowing the interpretation Bunting has in mind. This explanation would, however, depend on the existence of Irish dialects which behave like Scottish ones in this matter, and where the genitive case of leagadh might be leagaidh; I know of no such dialect.
To sum up, it is not clear how exactly the term téad leagaidh gets the meaning Bunting claims for it.
Colm Ó Baoill 2002