While I am on mobile and (therefore) have not accessed the files, the ToC and description of the OCR process leads me to understand that the original print is in Irish, not English.
Here's my Translations of the Chapter titles. I'm pretty sure many of these have old-Irish style séimhiú (a dot above a consonant denotes what would now be a h after the consonant) in the originals that have not been translated by the OCR, so there are several missing h letters. If I weren't on a plane over Afghanistan, I'd download the PDF to check. Will update the repo when I can!
Pláinéid na feaca Súil Duine riamh = A planet no person's eyes have ever seen
An Radarc, tríd an gCiandracán = the view throughout the [Ciandracan] (this is a compound proper noun, "Cian" is "head" or "brain" and "racán" could be visor or rocket)
An Turas go Manannán = the Trip to Manannán
Manannán = Manannán (it's a noun, which is very similar to the Irish term for the Manx and the Isle of Mann).
Muintear Manannáin = the people of Manannán
na 'Cráidmí' = the Craidmi (I think it's just a plural noun)
An tÁrd-Máigistir = the high Magistrate, or possibly the supreme magistry
An Priorún = the Priory
Oidce sa Coill = The class/lesson/teaching in the woods/forest
An tinneall = the fire
Oidce tar Oidceanta = Lesson upon lesson
Lug Lám-fada = the long-armed lug
An Tróid leis na 'Cráidmí' = The war with the Craidmi
Diogaltas = Revenge
An téalod = not sure about this one> Oidce tar Oidceanta = Lesson upon lesson
I suspect these are actually mistranscribed by the project. That looks more like it should be "Oiḋċe sa Coill" or "Oidhche sa Choill" without the ponc séimhithe, and in modern spelling "Oíche sa Choill" - "A Night in the Forest". Comparing the transcription of the first chapter with the source in the PDF they're missing a fada (an acute accent for non-Irish speakers) in "ná".
Similarly, I'd probably render the second one as "Night upon Nights".
The battle/fight with the Craidmi. troid is singular whereas war is plural.

Digitization of Manannán, written in 1940 by Máiréad Ní Ghráda. It is an Irish-language young adult sci-fi space travel book. It may contain the furst use of a Mecha outside of Japan. And the first mention of a gravity assist in literature. It has never been reprinted or translated. This is an attempt to make the book more accessible and more widely read.
The text used old Irish orthography (dot over letter = h after letter etc).
Pages 9–18 cover the start the first chapter (Pláinéid na feaca Súil Duine riamh). Page 13 appears in both files as a transition.
We are extracting and correcting the text step by step:
Errors are where the extract makes a spelling error . Do not worry about the page numbers and book name being present. These are easy to take out later. And help keep track of where we are in the book for combining the text together later.
| # | Chapter | Pages |
|---|---|---|
| 1 | Pláinéid na feaca Súil Duine riamh | 9–17 |
| 2 | An Radarc, tríd an gCiandracán | 18–30 |
| 3 | An Turas go Manannán | 31–43 |
| 4 | Manannán | 44–52 |
| 5 | Muintear Manannáin | 53–67 |
| 6 | na 'Cráidmí' | 68–75 |
| 7 | An tÁrd-Máigistir | 76–86 |
| 8 | An Priorún | 87–97 |
| 9 | Oidce sa Coill | 98–109 |
| 10 | An tinneall | 110–123 |
| 11 | Oidce tar Oidceanta | 124–136 |
| 12 | 'Lug Lám-fada' | 137–150 |
| 13 | An Tróid leis na 'Cráidmí' | 151–165 |
| 14 | Diogaltas | 166–177 |
| 15 | An téalod | 178–188 |
If you spot errors in the extracted text, please open an issue or submit a pull request. Corrections are especially welcome from Irish speakers.
The line between folklore and mythology is fuzzy, but this definitely falls on the mythology side of the line.
Not a native speaker myself, just a former gaelscoil student who's done their best to undo the gaelscoilis tendencies. Probably closer to a "heritage speaker" in the linguistic sense in some aspects.
Sadly out of practice these days, since I've been living in Denmark nearly three years. It's strange to lose competency in a language that you spoke every day for about 13 years.
I hope the project can upload a full scan at some point. I'm a huge sci-fi fan, and there's definitely a dearth of Irish language books in that genre.