160. Q.—­Will you explain the arrangement of the revolving grate?

A.—­The fire grate is made like a round table capable of turning horizontally upon a centre; a shower of coal is precipitated upon the grate through a slit in the boiler near the furnace mouth, and the smoke evolved from the coal dropped at the front part of the fire is consumed by passing over the incandescent fuel at the back part, from which all the smoke must have been expelled in the revolution of the grate before it can have reached that position.

161. Q.—­Is a furnace with a revolving grate applicable to a steam vessel?

A.—­I see nothing to prevent its application.  But the arrangement of the boiler would perhaps require to be changed, and it might be preferable to combine its use with the employment of vertical tubes, for the transmission of the smoke.  The introduction of any effectual automatic contrivance for feeding the fire in steam vessels, would bring about an important economy, at the same time that it would give the assurance of the work being better done.  It is very difficult to fire furnaces by hand effectually at sea, especially in rough weather and in tropical climates; whereas machinery would be unaffected by any such disturbing causes, and would perform with little expense the work of many men.

162. Q.—­The introduction of some mechanical method of feeding the fire with coals would enable a double tier of furnaces to be adopted in steam vessels without inconvenience?

A.—­Yes, it would have at least that tendency; and as the space available for area of grate is limited in a steam vessel by the width of the vessel, it would be a great convenience if a double tier of furnaces could be employed without a diminished effect.  It appears to me, however, that the objection would still remain of the steam raised by the lower furnace being cooled and deadened by the air entering the ash-pit of the upper fire, for it would strike upon the metal of the ash-pit bottom.

163. Q.—­Have any other plans been devised for feeding the fire by self-acting means besides that of a revolving grate?

A.—­Yes, many plans, but none of them, perhaps, are free from an objectionable complication.  In some arrangements the bars are made like screws, which being turned round slowly, gradually carry forward the coal; while in other arrangements the same object is sought to be attained by alternately lifting and depressing every second bar at the end nearest the mouth of the furnace.  In Juckes’ furnace, the fire bars are arranged in the manner of rows of endless chains working over a roller at the mouth of the furnace, and another roller at the farther end of the furnace.  These rollers are put into slow revolution, and the coal which is deposited at the mouth of the furnace is gradually carried forward by the motion of the chains, which act like an endless