Wood as commonly hewn, sawn, and planed; bricks as usually molded; stone as it leaves an ordinary hammer, all have flat sides and square edges. Hence it has been easiest to build walls and floors which meet at right angles, and to leave sharp corners on outer walls, windows, doorways, and chimneys. This is being changed for the better; in staircases the boards on which we tread and those which join them together now meet in smooth curves; so do the walls of rooms as they reach ceilings and floors, conducing to ease and thoroughness in sweeping and cleansing. In outer walls, in doorways and windows, similar curves reduce liability to hurt and harm. A wagon wheel easily knocks pieces from an angle of brickwork; it makes little impression on bricks retiring from the street line in a sweeping curve, as in the Madison Square Garden, New York. Factory chimneys have long been built round instead of square; to-day in the best designs the ducts to a chimney are also freely curved. In blast furnaces this is the rule for every part of the structure, ensuring gain in strength, lessening resistance to the flow of gases, and thus saving much fuel. When waterpipes varying in diameter are joined, the junction should be a gradual curve, otherwise retarding eddies will arise, wasting a good deal of energy; the same precaution is advisable in laying pipes for steam or gas. The elbows of pipes for gas, steam or water exert the least possible friction when given the utmost feasible radius. All the various parts of heavy guns are curved, since any sharpness of angle at a joint brings in a hazard of rupture under the tremendous strains of explosion. [Illustration: Corner Madison Square Garden, Madison Avenue and 26th Street, New York.] [Illustration: Two pipes with funnel-shaped junction.] Embossing and stamping machines may either decorate a sheet of note paper or make a tub from a plate of steel. Whatever their size these machines have the edges of their dies nicely rounded, so as to avoid tearing the material they fashion. To ensure the utmost strength in the machines themselves they are contoured in ample curves. In hydraulic presses, subjected to strains vastly greater, the same shaping is imperative, otherwise a cylinder may part abruptly with disastrous effect. So, too, in the manufacture of magnets and electro-magnets, their terminals are well rounded to ensure the closest possible approach to uniformity of field and of working effect.