OF RAIL-ROADS.

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engiues, in producing the same effect, is as25 34 :2101, which shews the saving of fuel, byincreasing the surface of the water exposed tothe action of the fire, in the ratio of 32 : 40.

Knowing this, it need scarcely be added,that, in every case, the consumption of fuelin these engines will, in some measure, dependupon the extent of surface exposed to theaction of the fire. This, no doubt, arises fromthe intensity of the heat necessary in narrowtubes to keep up a constant supply of steam,producing a more rapid combustion of the fueland throwing it off imperfectly consumed. Inwider tubes, the intensity is diminished, andthe fuel undergoes a more perfect combustion,and thus produces a greater effect.

The knowledge of this fact will unquestion-ably lead to a further diminution in the con-sumption of the fuel, even in the same engines.It would not, therefore, perhaps be treatingthe subject fairly, to fix at present the basis ofactual consumption for the performance of adefinite quantity of work ; as, however, theratio of saving can at any time be applied toany particular quantity fixed upon, I shall,consequently, give the result of the consump-tion, as deduced by the foregoing experiments ;but, first of all, I shall ascertain the relativequantity with different loads.