Jay C. Whitecloud has brought to my attention a paper by Professor Miles Lewis where he states that the earliest written mention of the term Dragon Beam was in
Old Cottages and Farmhouses in Surrey by W. Galsworthy Davie & W. Curtis Green when this was first published by B. T. Batsford in London in 1908.
On page 29 of the book Curtis Green provides a cutaway sketch of the upper floor framing including a Dragon Beam of The Old Butcher's Shop, Lingfield, Surrey.
I visited this building when preparing my Masters dissertation on
"old timber-framed buildings in South West Surrey" and took a number of "timber intense" photographs of The Old Butchers shop. Please note the blocked up (white) shop windows on the ground floor.
Ken Hume