My transcription is based on two manuscript autograph copies of Perry's Essay. One was brought to Britain by John Geddes (1735–99), whom Perry had helped set up the Scots College in Valladolid. This was until recently the property of the Scottish Catholic Archives in Edinburgh (MS P/5/10), and is now housed in the historic collection at Aberdeen University. The second is in the library of St Alban's College, Valladolid, Spain (MS Henson Legajo 18.1). M. E. Williams was of the opinion that the Valladolid copy is a second version since he regards its preface as a retort to Challoner's reaction to the first (Scottish) recension. This is not the opinion of the present editor. The Valladolid version is longer than the Scottish one and it has the appearance of a first draft that was later redacted. It is also a good deal untidier, with many deletions, illegible writing, unorganised referencing, as well as a general lack of presentation. The version housed at Aberdeen is not only better organised and presented, but there are numerous occasions when its written style represents an improvement. It is also the copy that has the responses of a Fr George Bishop and Challoner pasted into its first pages, suggesting that this is the manuscript that they had read and was intended for publication. These letters are pasted into the cover of the Aberdeen Manuscript. Challoner's letter might be dated to around 5 April 1766, because it is accompanied by Fr Bishop's letter which carries this date. Bishop was in charge of one of the oldest post-Reformation Catholic churches in England, at Brailes in Warwickshire. His letter is more positive than Challoner's, though he also seems anxious to confer with Perry, 'upon some remarks I have made'. Both would certainly have experienced a great deal of difficulty reading the Valladolid manuscript. It is hard to say with any certainty, but it is my conjecture that the Valladolid version is Perry's rough draft for the Scottish version that was produced for publication. In the production of this transcript I have used both manuscripts to produce a single whole Essay, complete with material missing from the Scottish version. The missing material that has been added is marked at the beginning and end with ^.

Both manuscripts are bound quires. I have endeavoured to transcribe them as accurately as possible saving the following changes.