When the barometer is “going up,” it means that the air pressure is increasing and in general this means a clear sky and fair weather.

When it “falls” this means that the air pressure is decreasing and rain is likely. The faster it falls, the more serious the rain that will probably follow, and the lower it falls, the more violent the weather is going to be. The lowest atmospheric pressure that has even been measured at sea level was in the eye of a hurricane, and you know how bad that weather can be!

What is normal for California? The same as everywhere else. Since the state has a reputation for being the “sunshine state” my guess is that you have a lot of days each year with high barometric pressure.

As for causing problems for pregnant ladies, I think that if the air pressure falls fast enough they might feel more discomfort than a non-pregnant person would, but only because they are already starting off less comfortable than most of us anyway. I don’t think there is any correlation between barometric pressure and the symptoms of mental disorders.

You know that feeling you get in airplanes and in cars going up and down mountains – that feeling that your ears are “popping?” That’s due to a change in air pressure. If you took a little hand-held barometer with you on those trips, you could watch the needle move down when you gained altitude and the air pressure fell, and then watch it go back up as you descended and the air pressure rose.

Water-based barometers

This concept of “decreasing atmospheric pressure predicts stormy weather” is the weird basis for a primitive weather prediction device called a weather glass or thunder glass. It can also be called a “storm glass” or a “Goethe barometer” (the writer Goethe popularized it in Germany). It consists of a glass container with a sealed body, half filled with water. A narrow spout connects to the body below the water level and rises above the water level, where it is open to the atmosphere. When the air pressure is lower than it was at the time the body was sealed, the water level in the spout will rise above the water level in the body; when the air pressure is higher, the water level in the spout will drop below the water level in the body. A variation of this type of barometer can be easily made at home

Mercury barometers

A standard mercury barometer has a glass column of about 30 inches (about 76 cm) 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. High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir. Since higher temperature at the instrument will reduce the density of the mercury the scale for reading the height of the mercury is adjusted to compensate for this effect according to the indication of a mercury thermometer included in the instrument case.

The first barometer of this type was devised in 1643 by Evangelista Torricelli. Torricelli had set out to create an instrument to measure the weight of air, or air pressure, and to study the nature of vacuums. He first used water, but it required a glass tube 60 feet long. He then used mercury, perhaps on a suggestion from Galileo Galilei, because it is significantly denser than water. Creating a vacuum with mercury takes less than three feet, which makes its use more practical than a water barometer.

Torricelli documented that the height of the mercury in a barometer changed slightly each day and concluded that this was due to the changing pressure in the atmosphere. He wrote: “We live submerged at the bottom of an ocean of elementary air, which is known by incontestable experiments to have weight”.

The mercury barometer’s design gives rise to the expression of atmospheric pressure in inches or millimeters (torr): the pressure is quoted as the level of the mercury’s height in the vertical column. 1 atmosphere is equivalent to about 29.9 inches, or 760 millimeters, of mercury. The use of this unit is still popular in the United States, although it has been disused in favor of SI or metric units in other parts of the world. Barometers of this type normally measure atmospheric pressures between 28 and 31 inches of mercury.

Design changes to make the instrument more sensitive, simpler to read, and easier to transport resulted in variations such as the basin, siphon, wheel, cistern, Fortin, multiple folded, stereometric, and balance barometers. Fitzroy barometers combine the standard mercury barometer with a thermometer, as well as a guide of how to interpret pressure changes.

On June 5, 2007, a European Union directive was enacted to restrict the sale of mercury, thus effectively ending the production of new mercury barometers in Europe.

Aneroid barometers

An aneroid barometer uses a small, flexible metal box called an aneroid cell. This aneroid capsule(cell) is made from an alloy of beryllium and copper.[2] The evacuated capsule (or more usually capsules) is prevented from collapsing by a strong spring. Small changes in external air pressure cause the cell to expand or contract. This expansion and contraction drives mechanical levers such that the tiny movements of the capsule are amplified and displayed on the face of the aneroid barometer. Many models include a manually set needle which is used to mark the current measurement so a change can be seen. In addition, the mechanism is made deliberately ‘stiff’ so that tapping the barometer reveals whether the pressure is rising or falling as the pointer moves.

A barograph, which records a graph of some atmospheric pressure, uses an aneroid barometer mechanism to move a needle on a smoked foil or to move a pen upon paper, both of which are attached to a drum moved by clockwork.

I know that my back hurts when there is a storm near by. The air pressure changes.

TMD