Vertical and Horizontal Lines and Planes

If an object is suspended by a string, the line of the string would pass through the centre of the earth; the line is called a vertical line. Any plane which contains a vertical line, e. g. the surface of the wall of a room, is called a - vertical plane. When a bricklayer is building a wall, he uses a plumb-line, which consists of a small lump of lead at the end of a string to test whether the surface of the wall is a vertical plane.

Any straight line which is perpendicular to a vertical line is called a horizontal line, and if all the lines that can be drawn in a plane are horizontal, the plane is called a horizontal plane, e. g. the surface of still water in a tank.

A surface is called level if it is part of a horizontal plane. You can test whether the floor of this room is a horisontal plane by using an instrument called a spirit-level, in which the adjustment to the horizontal is shown] by the position of a bubble in a glass tube containing (alcohol. If a line or plane is neither vertical, nor horizontal, it is called oblique. The words perpendicular and vertical must not be confused.

Two intersecting lines are perpendicular if they form a right-angled corner; a line is vertical if it points to the centre of the earth.

level уровень, плоская поверхность

oblique косой, наклонный

plumb-line отвес, нивелир

right-angled corner прямоугольный угол

spirit-level спиртовый уровень, ватерпас

tank бак, цистерна

test испытывать, испытание