-------------------------------------------------------------- | Vanes. | Diameter of inlet Diameter of fans. |------------------------| openings. | Width. | Length. | -------------------------------------------------------------- ft. in. | ft. in. | ft. in. | ft. in. 3 0 | 0 9 | 0 9 | 1 6 3 6 | 0 10½ | 0 10½ | 1 9 4 0 | 1 0 | 1 0 | 2 0 4 6 | 1 1½ | 1 1½ | 2 3 5 0 | 1 3 | 1 3 | 2 6 6 0 | 1 6 | 1 6 | 3 0 | | | -------------------------------------------------------------- For higher pressures the blades should be longer and narrower, and the inlet openings smaller. The case is to be made in the form of an arithmetical spiral widening, the space between the case and the blades radially from the origin to the opening for discharge, and the upper edge of the opening should be level with the lower side of the sweep of the fan blade, somewhat as shown in Fig. 5. [Illustration: FIG. 5] A considerable number of patents has been taken out for improvements in the construction of fans, but they all, or nearly all, relate to modifications in the form of the case and of the blades. So far, however, as is known, it appears that, while these things do exert a marked influence on the noise made by a fan, and modify in some degree the efficiency of the machine, that this last depends very much more on the proportions adopted than on the shapes--so long as easy curves are used and sharp angles avoided. In the case of fans running at low speeds, it matters very little whether the curves are present or not; but at high speeds the case is different.--_The Engineer_. * * * * * MACHINE FOR COMPRESSING COAL REFUSE INTO FUEL. The problem as to how the refuse of coal shall be utilized has been solved in the manufacture from it of an agglomerated artificial fuel, which is coming more and more into general use on railways and steamboats, in the industries, and even in domestic heating. The qualities that a good agglomerating machine should present are as follows: 1. Very great simplicity, inasmuch as it is called upon to operate in an atmosphere charged with coal dust, pitch, and steam; and, under such conditions, it is important that it may be easily got at for cleaning, and that the changing of its parts (which wear rapidly) may be effected without, so to speak, interrupting its running. 2. The compression must be powerful, and, that the product may be homogeneous, must operate progressively and not by shocks. It must especially act as much as possible upon the entire surface of the conglomerate, and this is something that most machines fail to do.