After tea they made their first trial at smoke production.  Placing a layer of soot on each of the trays, with a couple of fire-lighters in the midst, they lit some straw soaked in paraffin, poked it through the holes, and began to treadle the machine round the yard, the farmer and his wife looking on at the door.  A considerable volume of smoke poured out of the tank, but when they pulled up, Mr. Trenchard said: