Lamps and Lenses: How Old Mackinac Point Shed its Light

What puts the light in a lighthouse? Until 1913, a single lamp provided the light for the beacon at the Old Mackinac Point Lighthouse.

This lamp is similar to the one used in the first decade of the lighthouse's existence. It  was eventually replaced with a brighter, electric light.

This lamp is similar to the one used in the first 20 years of the lighthouse’s existence. It was eventually replaced with a gas lamp and then an electric light.

This diagram shows how even a small amount of light from the lamp could be magnified using a number of prisms in a Fresnel lens. (Click to enlarge)

This diagram shows how even a small amount of light from the lamp could be magnified using a number of prisms in a Fresnel lens. (Click to enlarge)

Like most other lighthouses in the United States, Old Mackinac Point used a kerosene lantern not unlike those still found in many homes today. Keeper George Marshall’s duties included regularly fueling the lamp, as it burned over 5 ounces of kerosene per hour. A red glass lamp chimney originally produced a red light, helping sailors identify Old Mackinac Point. Both the kerosene lamp and red light were replaced in 1913, when the U.S. Lighthouse Service installed an incandescent oil vapor mechanism, which produces a white light similar to a modern camping lantern.

While the kerosene lamp itself shone brightly, a fourth-order Fresnel lens amplified the Old Mackinac Point light until it was visible to a distance of 16 miles. The lens contained a series of stacked magnifying glasses around its center, with each glass focusing the light from the one beneath it. Prisms ringed the lens above and below the magnifying glasses. These prisms caught and bent more light, focusing it into the central beam created by the magnifiers. The entire lens rotated around the lamp, creating a flashing signature (one flash every 10 seconds) unique to Old Mackinac Point.

Today in History: Old Mackinac Point Lighthouse Fog Signal Sounded

On this day in 1890, Keeper George Marshall sounded the fog signal at the Old Mackinac Point Light Station for the very first time. This first blast of the fog whistle signaled the completion of a project begun a year earlier. In March 1889, Congress passed two acts regarding the creation of a light station at Old Mackinac Point. The first formally established the Old Mackinac Point Light Station, while the second appropriated $5,500 for the construction of a fog signal.

This photograph from the early 1900s shows Old Mackinac Point Lighthouse and the fog signal building. The inset image shows the two steam whistles next to the boiler vent stacks.

The fog signal sounded on November 5, 1890 was mounted on a 20’ by 40’ corrugated iron building. Inside, two identical steam boilers and associated machinery powered 10” steam whistles, which were mounted above the roof of the building. Although only one boiler and whistle were used at a time, keepers maintained the second set of machinery as a backup system. To help sailors identify the Old Mackinac Point fog signal, the fog whistles automatically sounded in a unique pattern: a 5-second blast, followed by 17 seconds of silence, followed by another 5-second blast, followed by 33 seconds of silence. Other light stations sounded their own unique whistle signatures.

The U.S. Lighthouse Service replaced the original 1890 fog signal building with a brick structure in 1907. New boilers and whistles were installed in this building. The fog whistles at Old Mackinac Point may have sounded like this: Click here to listen to a steam whistle.

The fog whistles themselves were replaced by air horns in the 1930s. Click here to listen to the fog horns at Old Mackinac Point Click here to hear it.

Click here for more information or to purchase a copy of one of Mackinac State Historic ParksOld Mackinac Point Lighthouse publications.