No one will have failed to observe that frequently the floor bends in such a way that one part rises at a right angle to the plane formed by the floor and then the following section arranges itself parallel to the flatness, so as to provide a step to a new perpendicular, a process which is repeated in a spiral or in a broken line to highly variable elevations.
Ducking down and placing the left hand on one of the vertical parts and right hand upon the the corresponding horizontal, one is in momentary possession of a step or stair.
Each one of these steps, formed as we have seen by two elements, is situated somewhat higher and further than the one prior, a principle which gives the idea of a staircase, while whatever other combination, producing perhaps more beautiful or picturesque shapes, would surely be incapable of translating one from the ground floor to the first floor.
Step 1: Parts
set of stairs
to make a staircase.