A Revolving Light at Work
From a historical standpoint, the Chantry Light was not a revolving light but was a fixed beacon. Other Imperial Lights were revolving, however. (See chart of 1859 on Chantry Island Lighthouse Diagram Page). Some of these lights had an ingenious way of revolving. The lenses were very heavy and they could not be rotated easily. For example, first order lenses which were the largest could weigh up to 12,000 pounds. Second order lenses were very heavy too. The engineers floated these lenses on a "lake" of mercury which reduced friction to a minimum and allowed the turning of the lens with a minimum of mechanical effort. Since continuous power was not available, a gearing mechanism was contrived that depended upon a heavy weight that was suspended down the tower. Once raised to the top the weight and the gearing mechanism would turn the lens in a precise period that would allow mariners to know what light they were now viewing. Keep in mind that both the colour and type of light was vital for safety. For example, moving down a dangerous shore with fog pressing in upon them, it was crucial that mariners know what light they were viewing. For this reason lights were all different along a coast. Some were fixed, some revolving and some were illuminated with a distinct colour.
This is an example of a Java Applet. The idea is to allow programs written in Java to be downloaded from the WEB Server to your machine and then to execute locally. Most programming languages are written so that they "compile" into machine code. Once this is done they can only run on the class of machine that the compiler serves. That is, they become fixed in the machine language of the target machine. Java is an interpretive language which outputs byte codes that are handled locally by an interpreter that is part of your WEB Browser. The way the above Applet works is quite simple. There are a series of 13 images that are rapidly displayed once loaded onto your machine. There is, of course, a trade-off between smoothness of animation and download time so we've tried to make a compromise here.
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