Bible Clocks

Clocks as Mechanical Sundials

Mechanical clocks as we know them now are a relatively modern invention. Their purpose is to provide an indoor, all-season, mechanical measure of time.

If you go hunting for very old, antique clocks, you find original mechanical clocks that only have hour hands and are without minute hands. The reason is in part the original cost, but also because the purpose of a mechanical clock is to provide an equivalent to a sundial.

Since a sundial only has 1 hand, so, too, do original mechanical clocks only have an hour hand, since sundials is where mechanical clocks get their inspiration.

In order to see the similarity between a sundial and a clock, I've stripped the more recent additions to the mechanical clock from the illustration at left. The minute (and second) hand is gone. The minor divisions of the hour are gone. What remains is only the hour hand and the hour markers.

With this view the similarity between a mechanical clock and a sundial is more apparent. The hour hand on a mechanical clock is making a precise sweep, 1 time around the face every 12 hours, in a way similar to the movement of a sundial's shadow through the day.

Of course sundails are not circular. Sundials sweep off the hours in an arc based on the angle of the dial from the ground, the distance from the equator of the sundial and the season of the year. These variabilities are related to the movement of the earth through the seasons.

The variablity in the observed sunrise and sunset times is handled by sundials through their orientation relative to the earth's poles. The pointer on the sundial points due north, (or south, in the southern hemisphere) and the shadow cast by the dial is at its minimum at exactly noon.

The time of the day when the sundial marks noon is always 24 hours away from the next day's noon. Not that this invariant holds at all locations and through all seasons everywhere on earth.

It is also possible to time local noon through the use of any vertical object that casts a shadow. The shadow, say of a plumb line, is points at the earth's pole, and is minimum, at local noon.

Until the invention of Standard Time this is how all clocks were set. Indeed, the process of setting the clock is built into the clock face itself.

We look at the face as we look at setting clocks through the use of Standard Time.

Part 3: Standard Time

Phil Stone

August 22, 2006

Updated August 22, 2006