Mackinnon appears to have written some notes, perhaps in preparation to publish a textbook that he had possibly expected to title 'Celtic Philology'. This is the second part in the collection, but Mackinnon has labelled it (in error?) as the first part, which he has titled 'Sounds'. The notebook's contents have a lot of information about the latest linguistic theory at this time, as well as attempts to describe defunct Celtic languages, such as Gaulish, as much as extant Celtic languages at the time.