Re: equation of time

[JOHN DAVIS]

Dear Frank et al,

 

The earliest datable dial with an EoT scale in Britain is (I believe) the 1685 double horizontal dial by Henry Wynne for Staunton Harold in Leicestershire.  But Thomas Tompion had published a table for pasting in his longcase clocks two years before.  The data almost certainly came from the first Astronomer Royal, John Flamsteed.  Tompion himself also put EoT tables on some of his dials but he didn't usually date them - the earliest which is positively datable is around 1702 but there may be ones from the 1690s.

 

For further details, see:

J. Davis: ‘The Equation of Time as represented on Sundials’  BSS Bulletin, 15(iv), pp 135-144, (2003).

and

J. Davis: ‘More on the Equation of Time on Sundials’, BSS Bulletin, 17(ii), pp. 66-75, (June 2005).

 

The early scales were usually labled "Watch fast/slow" or "Clock fast/slow".  Generally, it is not until the start of the 19th century that mean time is given precedence by changing the labels to "Dial fast/slow" or, sometimes, "Sun fast/slow"

 

I would be interested to hear from list members who know of other early dials with EoT scales. I have a database of many EoT scales, both from early almanacs and from 17th and 18th century dials: it is possible to see the way in which the actual values on dials lagged behind the latest versions calculated by the astronomers.

 

Regards,

 

John Davis

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"Roger W. Sinnott" <[EMAIL PROTECTED]> wrote:

At 11:16 AM 10/12/2005 +0100, Frank Evans wrote:
>My question is: Was this, like Richardson's appendix in Mrs. Gatty's
>book, a first appearance of an equation of time line? Can anyone supply
>earlier earlier examples of such a line on dials either in the UK or
>elsewhere?

Frank and others,

I think the lack of equation-of-time indicators on dials before the mid-1800s has a simple explanation:
Sundial time was considered CORRECT, and the mean solar time shown by clocks WRONG (or, at least, a mere approximation).

For example, I have several English almanacs for the year 1714. One of them is The Ladies Diary: or, the Woman's ALMANACK. Next to many dates throughout the year, it has phrases such as:

"Watches 3 minutes, 49 seconds too fast"
"Watches have gained of the Sun 2 minutes in 8 days"
"Watches will be 14 min.! slower than a good Sun-dial"

Another one, John Wing's Almanack, says on the cover that it contains "an Equation Table, for the rectifying Pendulum Clocks and Watches." (Unfortunately, that particular table is missing from my copy.)

-- Roger


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Dr J Davis
Flowton Dials