Dear Arranroots: many, many thanks for your reply. Your caution about the number of r's in Arran is well advised. In this case, fortunately, the question is resolved in favor of Arran by Robert's obituary, printed in March 1908 in the Buffalo (New York, USA) Commercial Advertiser shortly after his death. It states that he "...was born on the island of Arran, off the west coast of Scotland ..."
Again, my thanks - I'll contact the museum -
Hermit