I notice that in Alexander Pope's poem, An Essay on Criticism (1711), lines 669-70, there is the following couplet:
In grave Quintilian’s copious works we find
The justest rules and clearest method join’d
So, I take it that to Pope, the words "find" and "join'd" rhymed. Of course, today these words do not rhyme. Find rhymes with "kind" and "rind" and "bind", whereas, "join" rhymes with "coin" and "loin", and the sound of "OI" is the same as in "toy" and is definitely different than the long I in "find".
What is the explanation for this? It seems strange that the diphthong OI would have the same sound as I in find, even in a historical period. Was that indeed the case?
(Note: before suggesting the idea that Alexandrian poetry has non-rhyming couplets, consider this research. ALL of Pope's couplets are meant to rhyme. Pope's couplets are known in theory as heroic couplets, and it is a feature of this type of poetry that the couplets are composed of perfect rhymes. See "The Heroic Couplet" by William Bowman Piper (1969). If you have questions about a perfect rhyme, or some doubt that heroic couplets are composed of perfect rhymes, that is the book.)