[The Saucepan Man]

Intersting thoughts davem, and they possibly explain why Tolkien used the phrase in reference to a Dragon-like firework (albeit one made by Gandalf). But the reference is still to my mind incongruous with the fiction of the story having been written by the Hobbits. Even if steam trains did exist in Mordor and Angband, they are surely unlikely to have been sufficiently common features of Hobbit vocabulary to be used in this way.