These letters are not eclipsed; the n of the eclipsing word disappears.
This was not always the case. Instead of in leaḃar, in a book, we often find in older Irish i lleaḋar; so for in ród we find irród ; for in muir, mmuir, for in niṫ, in nniṫ.
|ar leaḃar||our book|
|i leaḃar||(ă lou-' ăr), in a book|
|ar long||our ship|
|a seol||their sail|
Instead of continuing to say arn bád, our boat, in bád, in a bot, the speakers of Irish found it easier to say arm bád, im bád; by degrees these were pronounced arm ád, im ád, but to keep a record of the original word, we now write ar mbád ( ăr-maudh), i mbád ( ă maudh). Here again we see that the eclipsed letter, b, is not noticed at all in the pronunciation.
as in English