Range lights, consisting of paired towers, were developed to guide vessels into harbors and channels. The front light is low, while the rear light, some distance away, is much higher. When ship captains have these lights lined up, one on top of the other, they know that they are on a safe course.
The Kennebec River Light Station, in Arrowsic,
Maine are also known as the Doubling Point Range Lights. Built in 1908, it
is the only set of Range light in Maine, and was automated in 1989. The front
tower is only 21 feet high, the rear light is 13 feet tall. The two towers
are connected by a wooden walkway, and are 235 feet apart. Originally,
each held a fifth-order Fresnel lens, but these were removed in 1979.