Marine: Some questions about a McGregor chronometer

Discussion in 'Chronometers' started by Marco C., Nov 13, 2016.

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  1. Marco C.

    Marco C. Registered User

    Nov 13, 2016
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    Dear all, I am a new member of this forum. My name is Marco and I live in Milan, Italy. I am pretty naive about timepieces in general and marine chronometers in particular, but I would like to learn. Recently I bought a McGregor chronometer from an English dealer. I am puzzled by a few things and would like to get some help from the experts, if possible.

    1st question. The chronometer's number is J/5816. I wasn't unable to discover what the "J" means. Many McGregor's chronometers have an alphabetic prefix. As far as I understand, "K" typically refers to chronometers with Kullberg movements and "M" to Mercer. But "J"? I have been told my chronometer has a Mercer movement. How can I check this? (The movement's number is 5763.)

    DialFront.jpg

    2nd question. What kind of auxiliary compensation is a "Double Auxiliary"? (see the dial) Looking at the balance wheel, it seems to me a variation on a Poole's auxiliary. May it be an Eiffe's auxiliary?
    BalanceWheel.jpg

    Thank you for your attention.
    Marco
     
  2. Tom McIntyre

    Tom McIntyre Technical Admin
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    Aug 24, 2000
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    I do not really know the McGregor chronometers, but given the meaning of M and K prefixes, I would venture that J is for Johannsen.

    The balance appears to have Poole's auxiliary and Airy's Bar and I suspect that is the meaning of double auxiliary. Perhaps someone more familiar with this terminology will chime in.

    In any case, welcome to the NAWCC Message Board and good luck in your collecting pursuits.
     
  3. Marco C.

    Marco C. Registered User

    Nov 13, 2016
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    Thank you Tom, I had a look at Airy's Bar on Gould's book and you are probably right.

    M.
     
  4. Tom McIntyre

    Tom McIntyre Technical Admin
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    I think this chronometer is pictured here in another thread, but this is a pretty good view of Airy's bar.

    AirysBar.jpg DialSpecial.jpg BoxFrontSpecial.jpg
     
  5. Marco C.

    Marco C. Registered User

    Nov 13, 2016
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    #5 Marco C., Nov 13, 2016
    Last edited: Nov 13, 2016
    Thank you again, but I am not sure it's the same type of device. I don't have access to the chronometer right now and I cannot check directly, but here is another picture:

    BalanceWheel2.jpg

    It seems that there is no supplementary bar, and the two internal arms seem to be screwed to the balance rims. If this is the case it's something different (but tomorrow I'll check directly).
     
  6. Tom McIntyre

    Tom McIntyre Technical Admin
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    It does look different. The key point of Airy's bar is that the temperature compensation mid point can be shifted by moving the center bar with respect to the balance center bar. That allows the temperature compensation adjustment to not interfere with poise.

    The center arm on your balance looks very thick as well as the two spring loaded compensation weights being screwed into the arms. Perhaps one of our friends can come up with some documentation on what the theory behind it was.
     
  7. Dr. Jon

    Dr. Jon Registered User

    Dec 14, 2001
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    The dial number and movement number should match. Your balance has a double auxiliary. The three screws near the arms are the Pooles' auxiliary. This is usually applied to a simple bimetallic rim but yours has an inner steel extra section screwed in at one end and free at the other. That is the second auxiliary.


    Mercer's Book "Chronometer makers of the world "has a long section on McGregor serial numbers but I can not find any specific reference to yours. Many serial numbers in the Kullberg section are close and that auxiliary looks a lot like the kind of thing Kullberg was doing, but Mercers says his double auxiliaries were a combination of Poole and Eiffe's

    To answer your question directly the best information is in Mercer's book. You have a very interesting chronometer despite the dial issue. Yours is not listed as either Mercer or Kullberg. Johannson listing include numbers 5822 and 5823 for the year 1906, so the most likely maker, of the three, is Johannsen.

    I am puzzled by the dial and movement number not matching, it does describe the chronometer. I t may have been that way from when it was made.

    BTW I just looked it up and am not an expert so if a real expert has a different view from mine theirs probably correct.
     
  8. Marco C.

    Marco C. Registered User

    Nov 13, 2016
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    I'm not an expert either, but I think that the fact the number on the dial is different from the one on the movement is not a problem. I saw the same thing in other pieces. I think that 5763 is the number assigned by the maker of the movement (whoever he is), while J/5816 is the number assigned by McGregor to the whole piece. Looking at the balance more carefully it seems to me that it could indeed be a combination of Poole and Eiffe's.
     
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