In the 1850s the light was emitted from a system of oil or kerosene lamps. The light was concentrated and focused with a system of Fresnel lenses. In the 1850s the light was provided from a burning wick in a whale oil lamp. Later, as kerosene became available, the light was provided by burning kerosene. They typically used an Argand lamp which featured a hollow wick in a glass chimney for better, brighter, combustion with a silvered parabolic reflector behind the lamp to direct and intensify the light output. All oil fired lamps used burning wicks to make the light—giving rise to one of the lighthouse keeper's nickname as "wickies" as they spent a great deal of their time trimming the wicks on their lamps in order to keep them burning brightly with minimum sooting. In the 1850s their lights were rotated using clockworks, usually powered by falling weights attached to chains. Many lighthouses had vertical shafts in them so the weights could drop the height of the tower. This provided a longer time period before the weights would have to be pulled up again by the lighthouse keepers to power the rotation mechanism. Some had to be rewound as often as every two hours.