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Below is a huge (20’’ × 35’’) Louis XVI Antique French Barometer. Notice how the dial runs from 27 in the lower left to 28 at the center top to 29 in the lower right. And notice how, as you said, there are 12 divisions to the “pouce” (the French or Canadian inch), with major divisions at 4/12 and 8/12 indicated with 4’s and 8’s. However, you mentioned the number 5 indicated between the inches on your barometer, which suggests 10 divisions in each pouce, meaning that you have a more modern barometer. This may also mean that it uses a difference pouce. According to Wikipedia: Pouce, noun, masc, French for “inch” (literally “thumb”) as a unit of measurement. In France, le pouce du Roi “the Royal inch” measured about 27.142 mm (1.0686 modern inches). In Quebec, le pouce québécois “the Quebec inch” was assumed to be a Royal inch; however Canada legally defined it as 27.070 mm (1.0658 modern inches) Both of these old measurements were about 1 1/15 modern inches. In 1959, on a proposal by Canada, the US, Canada and other nations of the Commonwealth agreed to an inch as exactly 25.4 mm, which continues in the current usage. Traditionally, the pouce was divided into 12 sections (as you mentioned), but more recently into halves, quarters, eighths, sixteenths, etc (which is what I’ve always used here in America). Your barometer has 0.1 inch divisions obviously because the scientific community divides atmopsheric pressure into decimals (tenths, hundreds, etc), but I don't know when they started doing this. I can’t clearly see where your barometer fits into all this. Perhaps your barometer is dated, even if it’s only a patent date. I did find these instructions on the medfordclock.com website. You have an aneroid barometer. The term “aneroid” comes from the Greek a + neros, “without liquid” because the sealed bellows contain air (actually, a partial vacuum), and not liquid as old old glass ones did (and they also made scientific ones using mercury.)QuoteHow do I adjust my aneroid barometer?Aneroid barometers have a small screw on the back. With a flat blade screwdriver turn this screw in either direction slightly while looking at the indicator needle. It should move in one direction or the other, tap the barometer to see where the needle settles. Continue until proper pressure reading is obtained. Do not turn the screw counter-clockwise (to the left) too far since it could come out.
How do I adjust my aneroid barometer?Aneroid barometers have a small screw on the back. With a flat blade screwdriver turn this screw in either direction slightly while looking at the indicator needle. It should move in one direction or the other, tap the barometer to see where the needle settles. Continue until proper pressure reading is obtained. Do not turn the screw counter-clockwise (to the left) too far since it could come out.
The cork excludes an possible effect of the atmosphere (and I gave seen glass ones fused shut). At best this is an odd thermometer.
Geezer, do you mean that sufficient paths exist in cork to allow for a timely equalization of the pressure gradients that weather produces? I had wondered about this. I wonder how an open container of Fitzroy's Storm Glass solution inside a vacuum chamber would react in the prescribed manner to pressure variations.
The volume of a sealed glass tube will change very slightly with pressure, but it will change a lot more with temperature.Also the pressure inside the sealed tube will change much more with asmbient temperature temperature than with atmospheric pressure.There's also the interesting point that if they were not sealed the solvents would evaporate- the one that my folks got as a wedding present is still pretty much as full as ever.Is there any actual evidence that these things work?Perhaps someone could set up a weatherglass with a webcam.Hearsay of an anecdote from someone who sells them isn't scientific evidence.
Ive got hold of an old barometer but dont know how to set it. I know i have to know the current pressure of my area but don't under how this relates to my barometer. It has the number 5 printed at the 12, 9 and 3 o' clock postions on the dial, 29 at the 10 o'clock postion, 28 at the 7 o'clock position, 30 at 2 o' clock and 31 at the 4 o'clock position. Can anyone help??