French movement questions, pendulum markings, pouces + lignes

Discussion in 'General Clock Discussions' started by Peter Planapo, Sep 19, 2019.

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  1. Peter Planapo

    Peter Planapo Registered User

    Mar 23, 2019
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    Hi all,

    Here is a French movement in a Howell, James & Co (London) case, in style of the 1880s Aesthetic Movement. I bought it at a non-runner price with no pendulum. I saw 7 2 on the backplate, so prepared a rough-and-ready pendulum to give 8145 beats per hour (given by David LaBounty's very useful pendulum rates sheet).

    It was way too slow. I had to shorten the pendulum to 5 pouces 9 lignes to get it right (apologies for the horrible pendulum; I'll get round to making a nicer pendulum "one day", but it runs perfectly as it is). So what was the 7 2 and where's the 5 9?

    A couple of other things. All the French movements I've seen are round; this one has a very similar inside and front plate layout, but it's square. Is that quite common? And there's no maker's stamp; could this be at the request of Howell James, so that buyers wouldn't get distracted?

    Any input appreciated, thank you
    Peter

    20190917_002126 (Large).jpg 20190917_001418 (Large).jpg 20190907_175946 (Large).jpg 20190917_002016 (Large).jpg
     
  2. Burkhard Rasch

    Burkhard Rasch Registered User
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    Jun 1, 2007
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    the pendulum length indicated on the back plate is the "theoretical" pendulum length ,i.e. the length of a pendulum where the mass of the bob is thought to be concentrated in one (geometrical) point and the rod is defined as mass-less.
    Since a real pendulum rod has a certain mass that is located above the (theoretical) center of masses and the bob with its mass has an extension in vertical direction its length differs considerably from the theoretical length. Anyway these indications serve as a good starting point for the game of try and error..
    And yes,the sqare variant of the pendule de Paris movement is quiet common in french clocks.
    Best
    Burkhard
     
    leeinv66 likes this.
  3. Peter Planapo

    Peter Planapo Registered User

    Mar 23, 2019
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    Hi Burkhard and thanks for the reply. You are of course right, a real-life pendulum is different from the "perfect" point mass + weightless rod.

    But in my other French clocks, I have several, the BPH and the approx effective length (from middle of suspension spring to about the middle of the bob), have corresponded extremely closely with the values in David LaBounty's chart. This one is way off... as I say, the period corresponds to 5p 9l.

    A friend has suggested that the man responsible for punching the numbers had a bad hangover that day, or left his glasses at home.
     
  4. jmclaugh

    jmclaugh Registered User

    Jun 1, 2006
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    The usual position on the pendule de Paris movements for the pendulum length is at the centre of the base of the back plate, however they are not all marked thus. I would think the 7 2 on this one is nothing to do with the pendulum length. It is quite common to find no maker's mark on this type of movement. Btw you can buy French pendulums from clock suppliers which is a much easier solution than making your own.

    Howell James & Co. is listed in London & Paris circa 1860-90, clockmakers to the Queen.
     
  5. Peter Planapo

    Peter Planapo Registered User

    Mar 23, 2019
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    Your reply is loaded with good info. I found "French" pendulums at Cousins UK, some have a centre rating nut and some have it at the bottom. Which would be more appropriate? They are the same sort of price, very cheap in fact.

    Come to think of it, you must be right about the pendulum length as my other French clocks with pendulum info have it at the bottom, often straddling the pillar while this 7 2 is near the top.

    Clockmakers to the Queen eh? Her Majesty had great taste.

    Thanks!
     
  6. jmclaugh

    jmclaugh Registered User

    Jun 1, 2006
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    Personally I'd go with the one with the nut at the bottom as I find they are easier to adjust the length. If you don't have a key for the Brocot adjustment I'd get one as it makes fine adjustment very easy as removing the pendulum on these clocks isn't.
     

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