A Bewildering Barometer

I bought an old aneroid barometer at a local estate sale many years ago.  It still works well.
Full barom_0723 (2)The convex glass cover was cracked so I replaced it with a piece of very old window glass, after slowly drilling a hole for the pointer.

The aneroid mechanism became popular in the early 1900s.  It uses a sealed and flexible bellows chamber that changes size with variations in atmospheric pressure, instead of the mercury filled fragile glass tubes of older designs.

I thought the case must have been changed at some time because the face references a thermometer (“Thermomètre selon Réamur”) and yet there is none present.  There are no markings on the wood case other than a cryptic “#61” engraved in the back surface. But the dial is very interesting:Dial_0721 (2)

For many years I wondered, and have repeatedly asked guests, what the scale reading from “28” to “31”, and in divisions of 1/12s, could represent?  It must surely be inches of mercury – sea level atmospheric pressure is about 29.5 inches of mercury – but why would the scale be subdivided into twelfths instead of the usual tenths?  None could explain.

The language on the face is surprisingly all in French, although the fine print says “P. F. Bollenbach” and “Barrington, IL”– not a known US francophone location.

At last Philips’ friends, Geoff and Dave, with a little help from King Google, have cracked the code: Before Napoleon’s time, and France’s great conversion to the metric measurement system, it seems the French used an inch measure, called a “pouce” (not the similarly sounding “puce”. That is a French flea!) which they subdivided into 12 “lignes”.  A ligne began about 1,200 years ago with German button makers and was “…the measurement of a round wick, folded flat…”.  It is still used today by some button and snap makers, and a few French and Swiss watch people, according to Google.  Around the same time England was actually dividing their “inch” into 10 subdivisions.  The English inch was then defined as 3 medium size dry barley corn grains laid to end to end, but that turned out to be about 12.6% longer (depending no doubt on the year’s harvest!) than the French inch.

A recent estate sale (it’s hard work being retired!) yielded a fine 1969 Nicholas Goodison 388 page book, “English Barometers 1680-1860”, for a few dollars.  It shows a 1772 Ramsden mercury barometer with a dual scale of quote “..both English and French inches divided into 1/10in. and 1/12in. (i.e. 12 ’lignes’) respectively..”

Ramsden 1772_0728 (2)

The other scales on it are Fahrenheit and Réamur thermometers and a conversion scale.

The earliest example of 1/12 divisions that I can find is the scale on this beautiful Robert Hooke 1665 wheel barometer. The scale here somewhat mysteriously reads “M, N, O, P” for the main divisions, but each gap between letters is subdivided into sixths and twenty-fourths.  Hooke was not French but he did come from the Isle of Wight so perhaps there was a little vin rouge nearby to help his studies?
Hooke Wheel 1665_0725 (2)
The final evidence comes from eBay where a few hundred $ might get you this very fine 1749 Louis XVI instrument.  It also has 1/12 divisions in the scale.Ebay old Barometre 27-29 12 div_0584 (2)So it seems that very old French barometers used the 1/12 divisions when most of the English ones were using the 1/10 parts of their fine scale.  My, perhaps 50 to 100 year old, Illinois instrument appears to have used French wording and one twelfth divisions to give an antique air to a modern aneroid mechanism.  I note too that the face is simple printed paper rather than the engraved metal of genuine antiques. I shouldn’t complain, Goodison’s book says that for accuracy an old mercury barometer needs periodic maintenance by “boiling” (sic) the mercury to remove absorbed water and oxygen!

Isn’t it ironic that despite being partly decimalized before continental Europe (as shown by the tenths divisions on their old mercury barometers) England stubbornly held on to their colorful, but so confusing to me in my school days, non-decimal: fathoms, firkins, furlongs, fortnights, farthings, etc., etc.  (Did you know there are about 5,600 “scruples” in one “strike”, whatever they may be measuring?).  France dropped it’s “lignes” in Napoleon’s time and went metric, or so they claim.   But they have yet to fully adopt the ‘true’, internationally agreed decimal system, “S.I.” (System International).  Although France does agree with the rest of the world that the current inch is now exactly 25.4 mm, many French people will insist on writing it as “25,4 mm”  This can be very confusing if you want to write a dimension of say 1 meter plus 1/4 millimeter (or metres and millimetres depending on whereabouts you happen to float in the Atlantic ocean) in millimeters (thank you very much David for pointing out the ‘mm’ omission) into an international technical drawing:  in SI it should be written “1 000.25 mm”; in France it is often written “1.000,25 mm”; and here in the US it is typically shown as “1,000.25 mm”.  So no wonder that international space probe crashed into Mars a few years back, while trying to land, because its computer thought the planet’s surface was further away than it really was! When flying above the surface of planet Earth it is very important to know what your barometer is actually measuring because that is the instrument which gives you your height above ground.  On the ill-fated trip to Mars I imagine other types of instruments, than mercury filled barometers, were used but sadly they did not give correct final values!

6 thoughts on “A Bewildering Barometer

  1. Nice to find your nice write-up.
    I purchased my first antique aneroid barometer several years ago to correlate my sharp headaches with air pressure (they did!). I became hooked, and now own six others (Imperial and Metric). Having a small collection is excessive, but sort of like observing ocean waves working together in slow motion–I enjoy them all. I’ve only seen one other aneroid barometer with the ‘French Inch’ (“pouce”) scale–your article was both enjoyable and informative.

  2. Very bewildering and intriguing pieces.


    Actually, the barometer in question (bewildering-barometer) has a face dial of French origins with Spiral thermometer. Thermometre scale of René-Antoine Ferchault de Réaumur became obsolete/absolete. And probably aneroid movement.

    Réaumur used un-pure alcohol the temperature range was 0° Ré as freezing 80°Ré boiling.


    Réaumur scale
    “If you have a thermometer with a large bulb filled with alcohol
    (but not 200 proof, it’s mixed with water, who knows how much),
    and the zero of your scale is at the point where water freezes
    and it takes eight percent of the alcohol in the bulb and tube up to zero
    to expand with the temperature to the point where the alcohol boils,
    then you have duplicated the scale of de Réaumur.”
    The Réaumur thermometers were no good
    for temperatures greater than the boiling point
    of alcohol, which would depend on the kind of alcohol.
    And their large bulbs made them too big
    to fit under a tongue. Moreover, today, outside
    of certain cheesemakers in Italy and Switzerland,
    few could tell you how warm 25 °Ré is,
    (although I can say it wouldn’t be too far from 25 °C).

    You have not made a Réaumur scale
    by using a bulb of mercury and measuring
    eighty degrees to the boiling point of water,
    which apparently some have claimed to do.


    pictured here is a later version (probably press imprinted)
    https://www.williamwordantiques.com/product/wall-hangings/barometers/louis-xvi-style-gilded-barometer-with-black-eagles-france-ca-1840/ ( late modern mid 1840’s)
    earlier version
    earlier hand drawn face the two were manufactured before the aneroid (this one does not have Thermometre Selon Réaumur/Reaumur)

    An aneroid barometer is an instrument used for measuring pressure as a method that does not involve liquid. Invented in 1844 by French scientist Lucien Vidi, the aneroid barometer uses a small, flexible metal box called an aneroid cell (capsule), which is made from an alloy of beryllium and copper. WIKI

    I recently acquired one, unfortunately, the glass witch was already cracked but not shattered did not survive the handling through the USPS. Not knowing anything about it, lack of photos and description it was missing the mercury tube. drive for the wheel to dial as you can see (plate 2 Hooks wheel barometer parts A Thu H) of the original conversation.

    As the listing says needing TLC I think I can make it work as originally designed. do not want to convert to an aneroid movement that can be done easily.

    Here is the listing of what I acquired.


    The glass was not original it was flat with signs of replacement held from the inside of frame with plaster, showing patina from old age.
    thermometer still intact
    The original ink is very faded
    Shows sign of missing extension on the bottom and ” The oval frame is adorned with typical seasonal planting motifs with a sheaf of wheat and garlands flanking the sides.”

    still trying to make out the very fine print from underneath
    Thermometre Selon Réaumur (translated meaning)
    Thermometer According to Réaumur
    which is not visible in the rubylane.com/item

    Any information or links would be appreciated.

    It is in rough shape but only paid one third the price. the glass tube, float plunger, and weight are about $75 to 100 + the cost of the 5 to 7 ounces of mercury to fill the tube. Older wheel type dial or stick mercury barometers usually measure 32 or more inches high. Here is a stick type measuring 50 inches and quite pricey


    Unique triple scale thermometre
    A colored version of Réaumur in his shop

  3. ~~~~~~~~~~~ I still learn something every day, have never noticed about the 1/12 the markings, not that much into French barometers ” I am thinking of acquiring a very simple one it has three marked zones.
    mauvais temps / tendance / beau temps
    ~~~~bad weather / trend / good weather ~~~~~~~~
    it only has the pascal scale covering 700 to 790


    Many inventions happen by accident. So it was with the mercury barometer which Evangelista Torricelli, a physicist and mathematician from Florence, Italy in 1641 originally intended to measure elevation rather than predict the weather.

    Torricelli’s colleague, Vincenzo Viviani, actually performed the experiment which demonstrated the existence of atmospheric pressure the following year.

    M,N,O,P are the consecutive letters of the alphabet when inventors apply for a patent they usually use locations marked by letters, to explain terms or functions
    “Tempete” is on the Stormy side of the barometer. on the low side

    Translations of tempête
    noun tempeste
    Violente perturbation atmosphérique accompagnée de pluie ou de neige, de vents violents.
    en,storm tempest es, (tempestad) Latin,(tempestas)
    Violent atmospheric disturbance accompanied by rain or snow, violent winds.

    storm tempête, assaut, orage, ouragan, tourmente, grêle

    tempest tempête, orage, en,( thunderstorm) tourmente

    weather temps, tempête, brise en,( breeze)

    blast explosion , as (thundering/lightning), souffle, rafale, sonnerie, fête, tempête

    thunder / tonnerre, fracas, tempête, bruit de tonnerre, retentissement

    flaw / défaut, imperfection, faute, inconvénient, souffle, tempête

    foul wind / tempête, gros temps

    On the opposite side “tres sec” very dry, on the high side

    La hauteur correspondante de la colonne de mercure était gravée sur le cadran et le mot “Change” était inscrit à 29,5 pouces; “Rain”, “Beaucoup de pluie” et “Stormy” ont été insérés à des intervalles d’un demi-pouce du côté bas, et “Fair”, “Fair Set” et “Very Dry” du côté haut.

    the above was translated from the following
    The corresponding height of the mercury column was engraved on the dial, and the word “Change” inscribed at 29.5ins; “Rain”, “Much Rain”, and “Stormy” were inserted at half-inch intervals on the low side, and “Fair”, “Fair Set” and “Very Dry” on the high side.

    The abbreviated words Bau/TEMS & BauFIXE and TRESSEC respective meanings
    beau tems, beau fixe ,tressec
    beautiful weather, beautiful fixed, very dry

    You can see unabbreviated words in the following link
    the eight image is the front of the barometer


    What many people do not know is a barometer should be read according to outside temperature and humidity.

    Most electronic barometers are usually in temperature controlled environments these days

    The rate of the fall and rise of pressure have to e interpreted according to the humidity and air temperature.


    I have a small collection of barometers for my amusement.



  4. Very interesting. Units seem to be more complicated than one might think–a curious mixture of historical chances and fundamental principles. I believe the barleycorn unit is somehow related to shoe sizes to this day.

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