"The letter C marks the point where the vessel to be exhausted is attached." -Century, 1889

Mercury Air-Pump

"The letter C marks the point where the vessel to be exhausted is attached." -Century, 1889

A bookcase, or bookshelf, is a piece of furniture, almost always with horizontal shelves, used to store books. A bookcase frequently has doors that may be closed to protect the books, bookshelves are open-fronted. These doors are usually glazed, so as to allow the spines of the books to be read.

Adjustable Multi Level Bookcase

A bookcase, or bookshelf, is a piece of furniture, almost always with horizontal shelves, used to store…

An illustration of a two story house.

Two Story House

An illustration of a two story house.

An illustration of a two story house.

Two Story House

An illustration of a two story house.

Indicator that establishes the horizontal when a bubble is centered in a tube of liquid

Construction Level

Indicator that establishes the horizontal when a bubble is centered in a tube of liquid

A tool used to indicate whether a surface is level (horizontal) or plumb (vertical).

Spirit Level

A tool used to indicate whether a surface is level (horizontal) or plumb (vertical).

A device used for determining or adjusting something to a horizontal surface.

Tool Level

A device used for determining or adjusting something to a horizontal surface.

"In straight levers of the first kind, the fulcrum is between the power and the resistance, as in fig 1, where F is the fulcrum of the lever AB; P is the power, and W the weight or resistance."—Pettigrew, 1874

First Kind of Lever

"In straight levers of the first kind, the fulcrum is between the power and the resistance, as in fig…

This apparatus illustrates the principle stating that liquids tend to find their own level.

Vessels in Communication

This apparatus illustrates the principle stating that liquids tend to find their own level.

"By measuring the weight required to move the end cap of any of the shown tubes filled with water, it may be ascertained that the water required is only dependent on the level of water, not the weight." -Avery 1895

Water Pressure Independent of Vessel

"By measuring the weight required to move the end cap of any of the shown tubes filled with water, it…

"a, a, a, represents the water-level of a pond or reservoir upon elevated ground. From this pond a line or pipe is laid, passing over a bridge or viaduct at d, and under a river at c. The fountains, at b, b, show the stream rising to its level in the pond, a, at two points of very different elevation." — Wells, 1857

Water Level

"a, a, a, represents the water-level of a pond or reservoir upon elevated ground. From this pond a line…

"When any liquid is placed in one or more of several vessels communicating with each other, it will not come to rest until it stands at the same height inall of thw vessels. This principle is emobodied in the familiar expression 'Water seeks its level.' the principle is illustrated, on a large scale, in the system of pipes by which water is distributed in cities." -Avery 1895

Water Level in Multiple Connected Vessels

"When any liquid is placed in one or more of several vessels communicating with each other, it will…

The instrument called the water-level illustrates the principle of equilibrium in vessels communicating with each other.

Water-level

The instrument called the water-level illustrates the principle of equilibrium in vessels communicating…