Tubular Worm Conveyors.—These consist of cylindrical iron tubes with a continuous spiral fitted to the inner periphery, as shown in the Figure. When at work the cylinder revolves bodily round an imaginary axis, supported outside by suitable rollers. This type of conveyor does not strictly conform with the attributes given at the heading of his chapter, as the trough, though stationary laterally, is revolving, but it is essentially a worm conveyor, and is therefore included.