Inventions whose working principle is mechanical: a mechanism, linkage, structure or simple machine that does its work through motion and force rather than an electrical, chemical or biological process. Belongs here: foundational mechanisms such as the wheel, the gear, the pulley and the screw; power and motion devices such as the steam engine, the internal combustion engine, the automobile and the mechanical clock; everyday mechanical tools and instruments such as the printing press, the typewriter, the telescope, the microscope, the piano, the analytical engine, the abacus, the slide rule, the ball bearing, the safety pin, the safety razor, the stapler, the padlock, the zipper, the wristwatch, the fountain pen, the ballpoint pen, the nail, the wheelbarrow and the umbrella; and larger mechanical and structural devices such as the elevator, the escalator, the crane, the hydraulic press, air conditioning and the refrigerator, plus historical mechanical weapons and tools such as the catapult, the crossbow, the longbow, the cannon, the firearm and the machine gun, and mechanical recording and duplication devices such as the phonograph and movable type printing. Does not belong here: devices whose working principle is fundamentally electrical, grouped under Electrical Engineering, or a chemical reaction, grouped under Chemical Engineering, even where a mechanical housing surrounds them.