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Herbert Prinz wrote:

> I have heard this argument many times, but I am not convinced. Nearly all
> mechanical clocks have the dial mounted in the vertical plane. The majority of
> public sun dials were mounted on vertical walls of churches or other official
> buildings. The shadow on those rotates anti-clockwise in the northern hemisphere.
> Clocks hands do, in general, not simulate the movement of the shadow on a sun
> dial. (Not to mention the double speed of rotation.)


The double speed of rotation I must leave to others. It has never made
sense to me that the hour hand of my watch goes round twice in a single
diel period.

Clocks do, indeed, usually lie in vertical planes but the majority of
sundials do not. (Granted, some do and Herbert makes a good point that I
had missed: Their sense of shadow rotation is opposite to that of a
horizontal sundial.) There are a few surviving early clocks (large ones
in public buildings) with hands which move anti-clockwise. It would be
interesting to know whether that was a deliberate attempt to follow
vertically-mounted sundials in similar settings.

>>In short, "clockwise" is synonymous with "with the Sun" in the Northern
>>Hemisphere because "clockwise" is defined to be the way that the Sun
>>appears to move when seen from that Hemisphere (north of the Tropic anyway).
>>
>
> This sounds more plausible, but is a different explanation from the previous one.


Is it different? The apparent motion of the Sun around the horizon and
the apparent motion of a shadow cast by the Sun onto a horizontal
surface don't seem so different to me. Maybe Herbert and I just differ
over how formal a structure we are willing to class as a "sundial".

> Isn't it a question of which kind of projection seems more natural to the
> observer? In higher latitudes, the sun remains close enough to the horizon, so
> that we are willing to consider the whole picture  from "above". But when we read
> local apparent time with a nocturnal using some circumpolar stars, we readily
> admit that the "hands of the celestial" clock" turn anti-clockwise. And yet,
> nobody denies that the daily revolution is the same for sun and stars. Of course?

That really needs some serious investigation into the development of the
language, of clock technology and of ways of viewing the world. Maybe
the expression "with the Sun" reached common seamen from nautical
astronomers. Maybe early clockmakers had the Almighty's astronomical
clockwork in their minds when they designed Earthly equivalents.
However, without attempting any research, I'd suspect that viewing
rotation as with or against the Sun derived from average ploughmen
watching the shadows of trees sweep across their fields (and likewise
from the common experiences of other outdoor workers), while that same
common experience led directly to sundial designs (back at the time of
Stonehenge and almost certainly far, far earlier) and so on to clock
design. And, personally, I'd doubt that most observers of the daily
solar apparent movement viewed their geocentric universe from above.


Trevor Kenchington


--
Trevor J. Kenchington PhD                         Gadus@iStar.ca
Gadus Associates,                                 Office(902) 889-9250
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