Split 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.
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.
This 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.