What machine turned the first order Fresnel lens?
The original lens assembly, which rotated on a chariot at ½ rpm, was turned by three 150 pound iron weights suspended on a cable and dropping down the center. The cable was wound around a drum in the clockwork mechanism beneath the lens, which worked much like a grandfather clock. Each morning, the weights were slowly cranked by hand to the top and then released at dusk when the lamp was lit, causing the lens to rotate. The gears in the mechanism provided the leverage to turn the 1-½ ton lamp/lens assembly. The speed of rotation could be adjusted by a fan governor in the clockwork. A gentle hand push was used to start the lens rotating but, once it was in motion, it maintained its rotation until the weight reached the bottom of the tower and had to be rewound. Regulations required that the weight be rewound to the top of the tower every morning. In many shorter lighthouses, cranking was needed every few hours.
