A more recent improvement consists in the use of pneumatic means for removing the dust that is caused by the use of revolving brooms or brushes, such removal being effected by means of a hood that covers the area of the street beneath the body of the machine, and incloses an air exhaust, the sweepings being drawn through the exhaust mechanism and deposited in a receptacle for the purpose, or in some instances deposited in a furnace carried by the machine and there burned. In cities having hard, smooth, paved streets and sufficient municipal funds, the most effective, but most expensive way, has been found to keep a large force of men constantly at work with hoes, shovels, brooms, bags and carts, removing the dirt as fast as it accumulates. _Abrading Machines._ One of the most striking inventions of the century is the application of the sand-blast to industrial and artistic purposes. For ages the sands of the desert and wild mountain plains, lifted and driven by the whirling winds, had sheared and polished the edges and faces of rocks, and cut them into fantastic shapes, and the sands of the shore, tossed by the winds of the sea, had long scratched and bleared the windows of the fisherman’s hut, before it occurred to the mind of man that here were a force and an agent which could be harnessed into his service. It was due finally to the inventive genius of B. F. Tilghman of Philadelphia, Pa., who, in 1870, patented a process by which common sand, powdered quartz, emery, or other comminuted sharp cutting material, may be blown or driven with such force upon the surface of the hardest materials, as to cut, clean, engrave, and otherwise abrade them, in the most wonderful and satisfactory manner. Diamonds are abraded; glass depolished, or engraved, or bored; metal castings cleaned; lithographic zinc plates grained; silverware frosted; stone and glass for jewelry shaped and figured; the inscriptions and ornaments of monuments and tombstones cut thereon; engravings and photographs copied; steel files cleaned and sharpened, and stones and marble carved into forms of beauty with more exactness and in far less time than by the chisel of the artisan. The gist of the process is the employment of a jet of sand or other hard abrading material, driven at a high velocity by a blast of air or steam, under a certain pressure, in accordance with the character of the work to be done. The sand is placed in a box-like receptacle into which the air or steam is forced, and the sand flowing into the same chamber is driven through a narrow slit or slits in the form of a thin sheet, directly on to the object to be abraded.