Mr. Brunton had a patent in 1819 for a revolving firegrate of a similar kind; but whether Mr. Steel's was antecedent to it (as would appear from the dates given, together with the circumstances), we do not know. Mr. Brunton has, however, the credit of carrying his apparatus into successful use, and of having rendered it very complete. Among many judicious contrivances, may be noticed a revolving scraper, which gathered up the ashes as they fell upon the ash plate. In the following year, 1820, Mr. Brunton took out a second patent for improvements upon the former; these chiefly consisted in a mode of raising or lowering the furnace at pleasure, so as to diminish or increase the heat of the boiler as required; also in a new mode of feeding the fire. The shaft of the circular fire-grate upon which it revolves, is made to pass through a hole in a bearer of iron, built in the brickwork, and receives its support at bottom upon another bearer of iron, which is capable of sliding up and down in grooves, so as to elevate or depress the fire, by means of a rack and pinion, acted upon by a lever or winch.

Round the periphery of the circular grate is a double rim of sheet-iron, rising up three or four inches, the space between being filled with sand, so that when the grate is raised, another ring of iron, attached to the wall of the furnace, may fit into the groove and form a sand valve, to prevent the passage of air, and check the transmission of heat. Two or more passages, provided with sliding doors, are made through the brickwork, for the purpose of admitting a current of air to the top of the fire, in order to assist in igniting the smoke, if necessary. The fire feeder is shaped like a hopper, placed over the feeding hole, and the delivery aperture at bottom is capable of contraction or expansion, as may be required. Below this is a plate of iron, placed in an inclined position, and suspended upon pivots for the purpose of being agitated, in order to distribute the fuel equally upon the grate; there is also a shovel upon rollers, moved by means of a rod and chain actuated by the engine.

By the very equal distribution of the coal upon the grate, a thin fire and a sharp draft is maintained, owing to every piece of coal upon the grate being successively exposed to a current of the fire passing constantly in one direction across the grate; the continual dropping of the coal in minute quantities, instead of opening the door to charge as usual, produces a great advantage in convenience, besides a saving of fuel. The introduction of the coal is likewise completely governed by the steam generated, so as to admit no more for combustion than is actually needed for the due performance of the work of the engine. The whole apparatus acted independently of the skill or of the carelessness of the fireman. Small coal, of greatly inferior cost to that generally used, answers well with a furnace of this kind, and thereby effects an important saving. A thin fire with a sharp draft produces the maximum effect, because the greater the quantity of oxygen brought into contact with the coal in combustion, the greater heat is obtained.