What was the original optic in the 1870 tower?
Like most late 19th century lighthouses, this one used a Fresnel lens. Fresnel lenses were manufactured in a series of sizes or orders with first order being the largest, over 17 times as powerful as the smallest (6th order). In this case, over 1,000 prisms were used and, all told, about 2,500 lb. of glass and bronze made up the 12 foot tall first order assembly. Triangular prisms projected light into a continuous 360 degree beam, and, in this case, 24 bulls-eye lenses provided the flashes. The light has always been white; at other lighthouses, red and green have also been used (mainly harbor and range lights because color reduces the range of the beam).
