A Greater Light for Mariners! Fresnel and His Life-Saving Lighthouse Lens

A recent drive north of San Francisco to Point Reyes National Seashore with its famous Point Reyes lighthouse was enough to stir many emotions. California’s rocky and picturesque northern coastline is reason enough to make the trip, but the lure of its famous lighthouse proves irresistible.

Lighthouse[1]Point Reyes Lighthouse

The Point Reyes lighthouse is perched on a high, notoriously treacherous point of land that extends well into the Pacific Ocean from the main coastline. Many a ship found its final resting place on these rocky shores, going back to the time when sailing vessels and their intrepid sailors first plied the waters, here. The first on the scene was likely Sir Francis Drake who is believed to have safely landed immediately south of here in 1579 at what today is known as “Drake’s Bay.”

The Point Reyes lighthouse first lit its first-order Fresnel (pronounced fray-nel) light source on December 1, 1870. The oil-lamp used was nestled at the focal point of the 6,000 pound rotating Fresnel lens assembly, and its focused light could be seen all the way to the horizon on clear nights – roughly twenty-four miles out in the ocean. The weight-driven, precision clockwork mechanism which rotates the huge lens assembly once every two minutes sweeps a beam of light past a given point every five seconds, a beam that can be seen three or four times farther out to sea than previous lights – thanks to the revolutionary lens design of the French engineer/scientist Augustin-Jean Fresnel. Prior to Fresnel’s published treatise on light diffraction in 1818 and the subsequent appearance of his revolutionary lens design in 1823, lighthouses relied on conventional, inefficient and heavy glass lenses and mirrors to focus light. Fresnel lenses were soon universally adopted for lighthouses based their superior performance. The 6,000 pound first-order Fresnel lens assembly and clockwork drive installed at Point Reyes in 1870 was purchased by the U.S. Government at the great Paris Exposition in 1867.

IMG_5053Looking up into the Fresnel lens assembly and pedestal

Fresnel lenses are ranked in order of their size (focal distance from internal light source to lens), and range from first-order at approximately 36 inches to just under 6 inches for a sixth-order lens. Point Reyes is renowned as the windiest location on the Pacific Coast and the second foggiest in all of North America. Given those credentials and the treacherous rocky point on which it sits, the Point Reyes lighthouse certainly merited the biggest Fresnel lens obtainable!

Fresnel Engraving_BW_8X10_2Augustin-Jean Fresnel

Point_Reyes_Lighthouse_1871[1]

Edweard Muybridge photo – 1888
The domed Fresnel lens is clearly visible inside.

Linda and I were at Point Reyes celebrating our 49th wedding anniversary. Upon arriving at the lighthouse after 22 miles of driving from “town,” we were greeted with the warning that the path down to the lighthouse is comprised of 308 steps – (equivalent to a 13 story building) and that the “faint-of-heart” should not attempt the trip. We looked at each other, smiled, shrugged, and off we went. Though narrow, the cement steps are solid and shallow, so the trip back up was not bad!

Folks with fear-of-heights issues are NOT going to enjoy the stairs, however, as the light itself is perched high above the ocean on a treacherous ridge. In the old days, before there were stairs, the light-keeper occasionally had to get down on hands and knees on the rocky trail to complete the trip in howling winds and dense fog. Winds have been clocked higher than 130 mph at Point Reyes! After seeing the site, first-hand, it is easy to imagine just how difficult the light-keeper’s job was in the old days – keeping the light lit and the weight-driven clockwork running 24/7. The gravity-powered mechanism required “rewinding” every 2 ½ hours!

IMG_5069On the way back up!

Heading for the ShoalsHeading for the Shoals!

The terror of being “off course” in wild seas along a rugged coastline must have been overwhelming to seafarers. Lighthouses played a significant role in reducing the incidence of shipwreck for more than a century, but today’s GPS satellite navigational aids have all but rendered them superfluous. Among lighthouses that continue to operate today, the light source is a high-tech electric bulb within the lens, not an oil lamp. Many of yesterday’s Fresnel lens assemblies are relegated to static displays in a museum building adjoining the lighthouse in which they served. Point Reyes’ light remains in operating condition, still in its original position. The last of its resident “keepers” left Point Reyes in 1985. The lighthouse is now under the jurisdiction of the National Park Service.

As for Augustin-Jean Fresnel, the French hero of this scientific/seafaring drama: He died young in 1827 at age 39. Although honored in his day with membership in the prestigious Royal (scientific) Society of London and by its award of the prestigious Rumford Medal in 1824, his name is little known, today, outside of science. Anyone who visits lighthouses is bound to learn of him and his famous lenses, however, and of the importance of his work to both scientific-optics and seafaring. His name is engraved on the Eiffel Tower in Paris together with a long-list of other illustrious Frenchmen.

Two Fine Resources:

Short Bright Flash

IMG_2657

I recommend the recently published book by Theresa Levitt on the history of the modern lighthouse and Augustin-Jean Fresnel whose pioneering work on scientific optics and subsequent lens design influenced both science and seafaring.

The other book specifically on the Point Reyes Lighthouse is a beautifully rendered historical and photographic treatment of the subject by Richard Blair and Kathleen Goodwin. I was delighted to find this fine book when we were in the town bookstore. I purchased two copies at a very reasonable price!

IMG_2663

An example of the beautiful photography in my copy of The Point Reyes Lighthouse by Richard Blair and Kathleen Goodwin: The photo shows the interior of the Point Reyes first-order Fresnel lens with the modern electric light source(s) clearly visible. This book is published by Color & Light Editions which specializes in Point Reyes literature and art.

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