A recurring feature of early Gaelic harps is the presence of two strings tuned tothe same note in the tenor range. These adjacent unisons break the diatonic run. This page gathers evidence and citations which describe and name this phenomenon.

The Scottish antiquarian John Bell, collecting information about the early Gaelic harp tradition in the mid 19th century from the harper Patrick Byrne, wrote in his notebook:

From Mr Patrick Byrne.
The open on the bass string of the Violin is one of the Sisters on the harp. The next string below on the harp and it, were tuned in unison, for which reason they were called the sisters. These two unison notes are sumetimes called, and in ancient times were called, Ne Cawlee - or the companions. Afterwards they were called the Sisters.
The harp is tuned to the Sister note...

John Bell's Notebook, mid 19th century1

Another 19th century collector, Dr. James MacDonnell, also reports technical terms from Byrne:

I have learned from Pat Byrne, a harper, that all harpers prior to O'Neill, having taught only through the medium of Irish, must have had names for all the strokes or chords on the harp. The strings which are octaves to the sisters he said had others, which he said were called 'Gilli ni fregrach ni Kaulai', the servants to the answers to the sisters.

letter from James MacDonnell, mid 19th century2

Freagrach comhluighe and gilly caomhluighe appear in Bunting's tables. MacDonnell also writes:

... and this is the note which the Harpers, speaking English, call "Sisters" but their word "Kaulai" is not, in vulgar language, convertible literally into the word "Sister" which the Irish express by "Derfur" ...

letter from James MacDonnell, mid 19th century3

MacDonnell describes instruments belonging to other 18th century Irish harpers, counting their stringing and tuning by reference to the unison strings:

Fanning's harp had thirty-five strings, fourteen below and nineteen above the 'sisters' - the eleven upper strings of iron wire...
Black's had eleven below and twenty-one above 'Sisters'...
Rose Mooney's had thirteen strings below and eighteen above the 'Sisters'

letter from James MacDonnell, mid 19th century4

Edward Bunting in his 1840 book includes the word caomhluighe in his tables of Irish harp terminology. For the online edition of the table dealing with this term, including some notes by Colm Ó Baoill, click here.

caomhluighe,...caomhluighe,...lying together
Called by the harpers "The Sisters," were two strings in unison, which were the first tuned to the proper pitch; they answered to tenor G, fourth string on the violin, and nearly divided the instrument into bass and treble

Edward Bunting, Ancient Music of Ireland, 18405

Bunting gives a slightly different form of the word a few pages later, this time without reference to the unisons:

coṁ luiġe,  combh luighe,  equally stretched

Edward Bunting, Ancient Music of Ireland, 18406

The term, and its explanations, were noted by Edward Bunting in tuning and gamut charts in his field manuscripts from the 1790s. This is my hand copy from Queens University Belfast, MS4 12 f18v, which appears to be a source for the above printed examples. The unison Gs are labelled "caomhliughe".

ms12 hand copy

For more info see the Irish Terms ms page. Thanks to Ann Heymann for showing me this notebook page.

In other notebook charts, Bunting uses the word 'sisters' to label the two unison g strings, e.g. ms29 page 81 (f38r). Below is my hand copy; you can view a low-resolution facsimile of ms29 p.81 at Queens University website.
hand copy of ms29 f38r
Underneath it says 'harp always tuned by the Sisters'

Other charts which include the term 'sisters' can be seen on ms29 p.150, p.155 & p.156; a chart showing the unisons but without names is on p.153.

William McMurchy, a Scottish Gaelic poet, piper and harper in Kintyre in the 18th century, left many interesting manuscripts including a set of measurements of a Gaelic harp:

The number of Bass Strings including one of the Sisters — 15

William McMurchy's ms, mid 18th century7

In about 1690, the Cambridge scholar James Talbot compiled measurements and descriptions of many different musical instruments. His descriptions of Irish harps mention the unison strings:

instrument tuned gradually from highest treble to half       in 43 tune 21 gradually afterwards the 22nd is a unison (these two called a Wolf) from them bring the rest up gradually by octaves,
The Instrument tun'd gradually from the highest Treble to the middle insert then a Unison those two call'd a Wolf the rest arrived gradually thus supposing that in 36 strings the 1st is ggg the last ΓΓ which includes 5 octaves the Wolf shall be about C (if not g).

James Talbot's manuscript, c.16908

A story from South Ulster, probably from the 17th century, describes tuning of a cláirseach, using the word cobhlach to decribe some part of the tuning:

...chuir ar fordhealguibh na clairsighe e ionnus gur chuir a tiuin & a horgain & a cobhllacha do reir a cheile.

Eachtra ghruagaigh na creige agus na cruite ’s an tiompáin, between c.1520-17129

A poem attributed to ‘Earl Gerald’, a 14th century aristocratic Irish poet, starts as follows:

Ne eaddowme cawle zlas...

I cannot tune cawle...

Book of the Dean of Lismore, early 16th century9

In the medieval tale of Deirdre and the Sons of Uisneach, there is a section where Deidre speaks in poetry, about the sweetness of the singing of her dead companions. The wording is obscure but it seems to be talking about deep notes, middle notes and high notes, with coblach used for the middle ones:

Fogur tuinne toirm Noísi
Ba céol bind a bith-chlóisi.
Coblach Arddáin ro-po maith,
Andord Aindli dia úar-baith.

The voice of Naoise a heavy wave, sweet music for the ear. The coblach of Ardan is good, and the Andord of Aindli towards the sheiling.

Longes mac n-Uislenn, Book of Leinster, c. 12th century

Perhaps the earliest attestation of this word in a musical context comes in commentaries on a line of the poem written on the death of St Columba, which says that Ireland without Columba is like a church without an abbot, or a harp without ceis. The commentator is trying (not very succesfully) to explain what the mystery word ceis means.

Ar crot cen ceis.
Ceis ainm do cruit bic bis hi comaitecht cruiti móri h-ica seinm; no ainm do ṫarraing ar a mbi in leithrind; no ainm don delgain bic; no ainm dona coblaigib; no don trom theit

A harp without ceis.
Ceis is the name of a small harp which accompanies a large harp at playing upon; or the name of a nail on which the léithriu is fastened; or the name of the little pin; or the name of the coblaigib; or of the heavy string

Liber Hymnorum, c. 12th century10

Note: this page (and others on this site) uses old Irish script and lenition. If you see garbled text or error characters you might try downloading a Unicode font that includes characters for dotted consonants. Advice can be found here at SMO. For the Gaelic script I suggest downlaoding Vincent Morley's Bunchló. Any problems let me know.