The principle that a fire can be made to give more heat, and the fuel more economically burned, by means of a mechanically forced blast than by a chimney draft, has been thoroughly demonstrated bl Mr. F. B. Blanchard, of this city ; and when the heat which is not used in the boiler is made to superheat the steam, and afterwards heat the feed water, a still greater economy and consequent saving of fuel is obtained. The John Faron, a steamboat of 250 tuns, not built on a model adapted for high speed, has had Mr. Blanchard's improvements applied to her, and so well and economically is the fuel burned that a small six-inch stovepipe is sufficient to carry off the products of conbustion. A few days ago we had an opportunity of personally 'observiBg the value of this improvement on board this boat, during one of her ordinary passages from this city to Haverstraw, on the Hudsona distance of forty miles. She made this distance in 3t hours each way, at an expense of 1,375 Ibs. of fuel the forty milesa most astonishingly small quantity of coal for a boat of her size and build. She lies at the village of Haverstraw all night, and so well is the heat cared for and fostered that without firing up during twelve hours, the steam was kept up, and only lost about ten pounds pressure from six o'clock one evening to the same hour next morning. In a few weeks we shall give engravings and a full description of this valuable invention.