Way back in the late 1940's/early 50's we had a poem, performed round the camp fire, which had the intoned chorus "Om Mani Padme Um". I know all about the chorus and its derivations but can only remember a few verses, one of which is below. I have googled away at this but cannot locate the poem. Here is a verse:- "The climber in the lofty alp "May feel a tingling of the scalp. "This is not, as some declare, "Due to the rareness of the air." A reference for the full poem would be most appreciated.
Sorry to say I don't know the answer to your question, issy, but it still might be of some help to you yourself and other potential googlers to write HUM, not UM - that's the way the mantra is usually written, I believe. Good luck!