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"A piston and rod shown with attached weight. The valve, A, can be opened and closed as needed so that the piston can be moved." —Hallock 1905

Piston and Rod

"A piston and rod shown with attached weight. The valve, A, can be opened and closed as needed so that…

"Crank M raises and lowers the two pistons C and D. The valves allow only for air to be removed from chamber J with a cutoff valve at K. The mercury filled barometer L measures the pressure in J." —Quackenbos 1859

Double Barrel Air Pump

"Crank M raises and lowers the two pistons C and D. The valves allow only for air to be removed from…

A pump is a device used to move fluids, such as liquids or slurries, or gases. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure; they only displace fluid, causing a flow. Adding resistance to flow causes pressure. Pumps fall into five major groups: direct lift, displacement, velocity, buoyancy and gravity pumps, and their names describe the method for moving a fluid.

Mechanical Action Air Pump

A pump is a device used to move fluids, such as liquids or slurries, or gases. A pump displaces a volume…

"A machine for remobing air out of any given vessel, or forcing it in." — Williams, 1889

Air-pump

"A machine for remobing air out of any given vessel, or forcing it in." — Williams, 1889

"The principal part of the aneroid barometer is a cylindrical air-tight box of metal closed by a corrugated top of thin elastic metal. The air is exhausted from the box, which is then sealed. Evidently, the pressure of the air on the outside of the cover will cause the cover to curve inwards, as the space inside of the cover is void of pressure, until the resistance due to the elasticity of the cover, aided by the resistance of a spring beneath it, is equal to the force exerted by the air." — Hallock, 1905

Aneroid Barometer

"The principal part of the aneroid barometer is a cylindrical air-tight box of metal closed by a corrugated…

This barometer depends upon the changes in form of a think metallic vessel partially exhausted of air, as the atmospheric pressure varies.

Aneroid Barometer

This barometer depends upon the changes in form of a think metallic vessel partially exhausted of air,…

"From on pan suspend a hollow cylinder of metal t, and below that a solid cylinder a of the same size as the hollow part of the upper cylinder. Put two weights in the other scale pan until they sxactly balance the two cylinders. If a be immersed in water, te scale pan containing the weights will descend, showing that a has lost some of its weight. Now fill t with water, and the volume of water that can be poured into t will equal that displaced by a. The scale pan that contains the weights will gradually rise until t is filled, when the scales will balance again." —Hallock 1905

Archimedes Principle

"From on pan suspend a hollow cylinder of metal t, and below that a solid cylinder a of the same size…

"Showing how firm pressure may be made with the fingers to compress the branchial artery of the left arm. Some large superficial veins are also shown." — Blaisedell, 1904

Branchial artery

"Showing how firm pressure may be made with the fingers to compress the branchial artery of the left…

"The pressure of the atmosphere may be easily shown by the tube and piston. suppose there is an orifice to be opened or closed by the valve b, as the piston a is moved up or down in its barrel. The valve being fastened by a hinge on the upper side, on pushing the piston down, it will open by the pressure of the air against it, and the air will make its escape. But when the piston is at the bottom of the barrel, on attempting to raise it again, towards the top, the valve is closed by the force of the external air acting upon it. If, therefore, the piston be drawn up in this state, it must be against the pressure of the atmosphere, the whole weight of which, to an extent equal to the diameter of the piston, must be lifted, while there will remain a vacuum or void space below it in the tube. if the piston be only three inches in diameter, it will require the full strength of a man to draw it to the top of the barrel, and when raised, if suddenly let go, it will be forced back again by the weight of the air, and will stright the bottom with great violence." —Comstock, 1850

Atmospheric Pressure

"The pressure of the atmosphere may be easily shown by the tube and piston. suppose there is an orifice…

"Roller Bandage. Bandage, a surgical wrapper of some kind applied to a limb or other portion of the body to keep parts in position, exert a pressure, or for other purpose." -Vaughan, 1906

Roller Bandage

"Roller Bandage. Bandage, a surgical wrapper of some kind applied to a limb or other portion of the…

A homemade barometer made using a bottle.

Barometer

A homemade barometer made using a bottle.

"A Torricellian tube, firmly fixed to an upright support and properly graduated, constitutes a mercurial barometer. The zero of the scale is at the surface of the mercury in the cistern." — Avery, 1895

Barometer

"A Torricellian tube, firmly fixed to an upright support and properly graduated, constitutes a mercurial…

"The barometer is simply a pressure gauge that registers the pressure of the air. In this case the cup and tube at the bottom are protected by a brass or iron casing. At the top of the tube is a graduated scale. Attached to the casing is an accurate thermometer for determining the temperature of the outside air at the time the barometric observation is taken." — Hallock, 1905

Barometer

"The barometer is simply a pressure gauge that registers the pressure of the air. In this case the cup…

An instrument used to measure atmospheric pressure.

Barometer

An instrument used to measure atmospheric pressure.

An instrument used to measure atmospheric pressure.

Barometer

An instrument used to measure atmospheric pressure.

"Suppose a to be a long tube, with the piston b so nicely fitted to its inside, as to work air tight. If the lower end of the tube be dipped into water, and the piston drawn up by pulling at the handle c, the water will follow the piston so closely, as to be in contact with its surface, and apparently to be drawn up by the piston, as though the whole was one solid body. If the tube be thirty-five feet long, the water will continue to follow the piston, until it comes to the height of about thirty-three feet, where it will stop, and if the piston be drawn up still farther, the water will not follow it, but will remain stationary, the space from this height between the piston and the water, being left a void space or vacuum." —Comstock, 1850

Barometer

"Suppose a to be a long tube, with the piston b so nicely fitted to its inside, as to work air tight.…

A standard mercury barometer has a glass column of about 30 inches in height, closed at one end, with an open mercury-filled reservoir at the base. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir.

Barometer

A standard mercury barometer has a glass column of about 30 inches in height, closed at one end, with…

"...being merely a tube of glass, nearly filled with mercury, with its lower end placed in a dish of the same fluid, and the upper end furnished with a scale, to measure the height of the mercury." -Comstock 1850

Barometer

"...being merely a tube of glass, nearly filled with mercury, with its lower end placed in a dish of…

"The aneroid barometer is an easily portable instrument, and avoids the use of any liquid. It consists of a circular metallic box, exhausted of air, the corrugated diaphragm of which is held in a state of tension by springs." — Avery, 1895

Aneroid barometer

"The aneroid barometer is an easily portable instrument, and avoids the use of any liquid. It consists…

"Mercury enclosed in a tube inverted and inserted into a bath of mercury can serve as a measurement of the atmospheric pressure, as the height of the mercury in the tube must directly correspond to the weight of the air pressing down on the bath of mercury underneath it." —Hallock 1905

Mercury Barometer

"Mercury enclosed in a tube inverted and inserted into a bath of mercury can serve as a measurement…

"The degree to which the air has been exhausted from a closed vessel in which there is a partial vacuum is measured by the height to which a mercurial column in a vertical tube, whose top is connected to the vessel, will rise under the pressure of the atmosphere." —Hallock 1905

Barometer Measuring Pressure of a Partially Evacuated Vessel

"The degree to which the air has been exhausted from a closed vessel in which there is a partial vacuum…

This illustration shows a Blake Ore Breaker (stone crusher), used in a gold stamp mill. This crusher breaks the large, mined rocks containing the gold (ore) into small pieces, to then be reduced to the finest powder by stamps.

Blake Ore Breaker

This illustration shows a Blake Ore Breaker (stone crusher), used in a gold stamp mill. This crusher…

Uniting the theories of partial polygons of resistance and centres and lines of resistance, this buttress of blocks illustrates the tangential curve that is the line of pressures.

Buttress of Blocks

Uniting the theories of partial polygons of resistance and centres and lines of resistance, this buttress…

This apparatus is used to prove Boyle's Law which describes the relationship between the product pressure and volume within a closed system as constant when temperature remains at a fixed measure; both entities remain inversely proportional.

Proof of Boyle's Law for Expanding Air

This apparatus is used to prove Boyle's Law which describes the relationship between the product pressure…

"The carotid artery may be compressed by pressing the thumb or fingers deeply into the neck in front of the strongly marked muscle which reaches from behind the ear to the upper part of the breastbone." — Moss, 1914

Carotid compression

"The carotid artery may be compressed by pressing the thumb or fingers deeply into the neck in front…

This instrument consists of a bent tube closed at one end and containing within the space a quantity of air which is cut off from external communication by a column of mercury.

Compressed Air Manometer

This instrument consists of a bent tube closed at one end and containing within the space a quantity…

Pressure cooking is a method of cooking in a sealed vessel that does not permit air or liquids to escape below a preset pressure. Because the boiling point of water increases as the pressure increases, the pressure built up inside the cooker allows the liquid in the pot to rise to a higher temperature before boiling.

Steam and Water Cooker

Pressure cooking is a method of cooking in a sealed vessel that does not permit air or liquids to escape…

A cup of water next to a jar, with a tube running between the two.

Cup and jar

A cup of water next to a jar, with a tube running between the two.

A storm composed of sand. It occurs when the air over the sand becomes hot, and rises. The differences in air pressure and temperature allow the cooler winds to rush in.

Dust Storm

A storm composed of sand. It occurs when the air over the sand becomes hot, and rises. The differences…

The pressure on the bottom of a vessel containing liquid is not affected by the breadth or narrowness of the upper part of the vessel.

Experiment of Pascal's Values

The pressure on the bottom of a vessel containing liquid is not affected by the breadth or narrowness…

"In the forcing-pump atmospheric pressure plays but a small part. There is no valve in the piston c, but the water raised through the suction-pipe a, and the valve g, is forced by each depression of the piston up through the pipe e e, which is furnished with a valve to prevent the return of the fluid." — Wells, 1857

Forcing-Pump

"In the forcing-pump atmospheric pressure plays but a small part. There is no valve in the piston c,…

"For measuring the gas concentration, pressure and temperature, use may be made of an apparatus of the type shown [here]." —The Encyclopedia Britannica 1910

Apparatus for Measuring Gas Concentration Pressure and Temperature

"For measuring the gas concentration, pressure and temperature, use may be made of an apparatus of the…

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg. The gas must be well-behaved during its compression (it must not condense, for example). The technique is slow and unsuited to continual monitoring, but is capable of good accuracy.

McLeod Gauge

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the…

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few mmHg. The gas must be well-behaved during its compression (it must not condense, for example). The technique is slow and unsuited to continual monitoring, but is capable of good accuracy.

McLeod Gauge

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the…

A hand holding up a tube from a larger, mercury-filled tube.

Hand and barometer

A hand holding up a tube from a larger, mercury-filled tube.

A hand holding a tube, with one end in a bowl.

Hand with tube

A hand holding a tube, with one end in a bowl.

A pair of hands holding a glass tube filled with a dark liquid.

Hands with tube

A pair of hands holding a glass tube filled with a dark liquid.

"The hydraulic ram uses alternating water pressure, air pressure, and suction to provide a steady stream of water through the delivery pipe, e." —Hallock 1905

Hydraulic Water Ram

"The hydraulic ram uses alternating water pressure, air pressure, and suction to provide a steady stream…

"Pumps water in bursts. Water enters pipe B and is forced into D then up the tube F. Any excess water in tube B exits through E." —Quackenbos 1859

Hydraulic Ram

"Pumps water in bursts. Water enters pipe B and is forced into D then up the tube F. Any excess water…

Water that is placed in an apparatus will have equal pressure if the pistons pushing on it push at the same time with the same frequency.

Hydromechanics

Water that is placed in an apparatus will have equal pressure if the pistons pushing on it push at the…

To monitor breathing gas pressure in the diving cylinder, a diving regulator usually has a high pressure hose leading to a contents gauge (also called pressure gauge). The port for this hose leaves the first-stage upstream of all pressure-reducing valves. The contents gauge is a pressure gauge measuring the gas pressure in the diving cylinder so the diver knows how much gas remains in the cylinder. It is also known as submersible pressure gauge or SPG.

Pressure Variation Indicator

To monitor breathing gas pressure in the diving cylinder, a diving regulator usually has a high pressure…

Tool for exerting pressure or lifting

Lifting Jack

Tool for exerting pressure or lifting

An image summarizing Pascal's law, which states that pressure of a liquid is equal in all directions provided that the pressure ratio is the same.

Pascal's Law

An image summarizing Pascal's law, which states that pressure of a liquid is equal in all directions…

"In the third order of lever the power acts between the prop and the resistance, where also P : W :: BF : AF, and the pressure on the fulcrum is P-W, or the power less the weight."——Pettigrew, 1874

Third Kind of Lever

"In the third order of lever the power acts between the prop and the resistance, where also P : W ::…

Logarithmic graph (smooth curve) modeling the law of expansion with values of volume and pressure.

Logarithmic Graph of the Law of Expansion

Logarithmic graph (smooth curve) modeling the law of expansion with values of volume and pressure.

"By means of the two hemispheres, it can be proved that the atmosphere presses upon a body equally in all directions. This device was invented by Otto Von Guericke, of Magdeburg, and is called the Magdeburg hemispheres." — Hallock, 1905

Magdeburg Hemispheres

"By means of the two hemispheres, it can be proved that the atmosphere presses upon a body equally in…

"Mercury manometer for recording blood-pressure. d g, glass U-tube partly filled with mercury. In one limb is borne a float, e, bearing a recording device f; the other limb is filled with a suitable liquid and connected water-tight with the heart end of a divided artery b, by means of glass connection a. Changes in the mercury level indicated changes of arterial pressure." —Martin, 1917

Manometer

"Mercury manometer for recording blood-pressure. d g, glass U-tube partly filled with mercury. In one…

"Rupture of a Mountain.—There is no doubt, but in the operations of nature, great effects are sometimes produced among mountains, by a small quantity of water finding its way to a reservoir in the crevices of the rocks far beneath. Suppose, in the interior of a mountain, there should be a space of ten yards square, and an inch deep, filled with water, and closed up on all sides; and suppose that, in the course of time, a small fissure, no more than an inch in diameter, should be openeing by the water, from the height of two hundred feet above, down to this little reservoir. The consequence might be, that the side of the mountain would burst asunder, for the pressure, under the circumstances supposed, would be equal to the weight of five thousand tons." —Comstock, 1850

Mountain Rupture

"Rupture of a Mountain.—There is no doubt, but in the operations of nature, great effects are…

The vertical rays are spread over a smaller area, and pass through a thinner layer of air. The vertical rays strike more directly, and, therefore, produce more heat.

Oblique Rays

The vertical rays are spread over a smaller area, and pass through a thinner layer of air. The vertical…

A gas holder is a metallic shell which is open at the bottom (like a bell), the lower edge of which dips into a deep tank of water in order to prevent the contained gas from escaping. The framework may be either of steel or timber -- the latter being preferred for the largest holders. This illustration shows a partial section of a typical large American gas holder. It is a 5,000,000 cubic foot holder in New York City.

Partial Section of Typical Large American Gas Holder

A gas holder is a metallic shell which is open at the bottom (like a bell), the lower edge of which…

"Pressure exerted anywhere upon a liquid inclosed in a vessel is transmitted undiminished in all direction, and acts with the same force upon all equal surfaces, and in a direction at right angles to those surfaces." -Avery 1895

Pascal's Law

"Pressure exerted anywhere upon a liquid inclosed in a vessel is transmitted undiminished in all direction,…

"...let the area of the piston a be 1 square inch; of b, 40 square inches. According to Pascal's law, 1 pound placed on a will balance 40 pounds placed on b." —Hallock 1905

Pascal's Law and Water Pressure

"...let the area of the piston a be 1 square inch; of b, 40 square inches. According to Pascal's law,…

A baroscope, which is a version of the barometer. It measures atmospheric pressure.

Pressure

A baroscope, which is a version of the barometer. It measures atmospheric pressure.

"The tightly fitted piston at the top of a glass vessel of water is driven down. The contained liquid is compressed and the pressure equally distributed through the glass and the water flows out of the tubes along the sides." —Quackenbos 1859

Pressure of Liquids

"The tightly fitted piston at the top of a glass vessel of water is driven down. The contained liquid…

In image a, the pressure at the bottom is the same as the pressure at the top of the cylinder. If the area at the bottom and the depth of the liquid of image b is the same as image a, then the pressures will be the same for both.

Downward Pressure

In image a, the pressure at the bottom is the same as the pressure at the top of the cylinder. If the…

No upward pressure is present on surface c because of because of the weight of the water in part c d. Upward pressure is present on c because of the weight of the water in part b c.

Upward Pressure

No upward pressure is present on surface c because of because of the weight of the water in part c d.…

"Get a lamp-chimney, preferably cylindrical. With a diamond or a steel glass-cutter, cut a disk of window glass a little larger than the cross-section of the lamp-chimney. Pour some fine emery powder on the disk, and rub one end of the chimney upon it, thus grinding them until they fit accurately...place [the chimney] under the water as shown. the upward pressure of the water will hold the disk in place. Pour water carefully into the tube; the disk will fall as soon as the weight of the water in the chimney plus the weight of th disk, exceeds the upward pressure of the water." -Avery 1895

Water Pressure Experiment

"Get a lamp-chimney, preferably cylindrical. With a diamond or a steel glass-cutter, cut a disk of window…

"After pouring mercury into the U-tube, the level of mercury is marked by a. c and e refer to the positions of the mercury after water has been added so that the water fills one side of the U-tube." -Avery 1895

Effects of Water on Mercury in a U-tube

"After pouring mercury into the U-tube, the level of mercury is marked by a. c and e refer to the positions…

"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…

"The vessel a is fitted with a wooden bock of the same size as, and free to move in, the cylinder; the vessel b is filled with water, whose depth is the same as the length of the wooden block in a. When a pressure is applied to a, the pressure will be transmitted to the bottom unchanged. However, when the same pressure is applied to b, the pressure is transmitted everywhere, as the molecules of water are free to move." —Hallock 1905

Water versus Wood Pressure

"The vessel a is fitted with a wooden bock of the same size as, and free to move in, the cylinder; the…