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November 17, 2009

Fresnel lens tune-up

Filed under: 100th Anniversary, Events, Observations — Lee Radzak @ 5:59 pm

3rd-order, Fresnel lens at Split RockSplit Rock Lighthouse has the last operational Fresnel lens in the country remaining in the lens room of a lighthouse that still operates on its original mercury float and is rotated by a clockwork mechanism.

Last week one of the few people in the country who can be considered an old-school ”lampist”, Jim Woodward, along with Kurt Fosberg, cleaned the mercury and made adjustments to the lens, float, and rotating mechanism.  Since mercury is a hazardous material special certification and special care and equipment is required to prevent exposure to mercury vapors during the process.

Draining mercury from lens float

Nearly two gallons of mercury was drained, and the mercury bowl and float cleaned, and the mercury replaced.  The very small surface area of mercury that is exposed to the air when the float is closed was covered with mineral oil to stop any mercury exposure to the air.

Mercury bowl and float of Split Rock lensThis was a fascinating procedure to watch especially in that the knowledge of the old classical lenses and their care is becoming a lost art.  This tune-up, along with restoration on the lighthouse itself, were completed in time for the 100 year anniversary of the commissioning of Split Rock Lighthouse which will be celebrated in 2010.

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  1. What a cool story. I love little details like this of what it takes to maintain history. Good job, Split Rock!

    Comment by Andrew Slade — November 17, 2009 @ 9:46 pm

  2. Those photos deserve a new display panel in the Fog Signal Building.

    Comment by Dave Carlson — November 19, 2009 @ 9:29 pm

  3. Wow! Those are fantastic photos. Great story. I’m such a sucker for lighthouses.


    Comment by Beth Blair — December 3, 2009 @ 12:13 pm

  4. I am searching for drawings, descriptions or plans of how the clockwork was constructed. Can anyone help me? When I was in my twenties (62 now) I began to dream of scaled-up clockworks and falling weight to power things. A few days ago at the Pidgeon Point Lighthouse was the first time I heard of an actual example; a mere 450 lbs. falling 25 ft. in 4 hours!

    I’d be most thankful if someone could link me to
    working drawings or similar.

    Comment by John Sears — July 12, 2010 @ 7:19 am

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