So, what did railroads, clock makers and financial institutions use for
accurate time before 1900? If you were in London, you could subscribe to
a service in which a lady carried a mechanical chronometer to the
Greenwich Observatory in the morning and then made a circuit to
subscribers, allowing them to reset their own clocks.
But, if you worked at a railroad station in England earlier, there was
no lady to carry a chronometer and no telegraphed time much before 1900.
Yet, British trains were scheduled with minute arrival/departure times;
the Brits were fanatical about trains being on time! So, what then was
used to set railroad clocks? And, how did folks in the countryside
determine time sufficiently accurately to meet their trains? Most
sundials can barely be read to five minutes, particularly ones common
folks could afford.
Enter the Dent Dipleidoscope. This was an inexpensive, easy-to-use
optical device that could identify local solar noon easily within tens
of seconds and, with care, within three seconds! For 1850, other than at
an observatory with a noon transit instrument, that was precision with a
capital P.
An antique authentic Dent dipleidoscope is currently offered for live
auction on eBay:
I noticed that a Dipleidoscope is up for live auction on Ebay (USA) - this
seems to be a rare offering (not in my budget!).
http://www.ebay.com/itm/DIPLEIDOSCOPE-/231365300840?ssPageName=ADME:SS:SS:US:3160
LOT 1130
Seller's Estimate: USD 600.0 - 800.0
DIPLEIDOSCOPE - England, 19th century, brass and bronze. Brass and glass prism mechanism inset into a shaped
bronze case with scrolled sides. Engraved "Dent's Patent Meridian Instrument" and "67 Strand,
London". 3"h. 2.25"w. 3"d.
Pricey, you say? Well, it is an authentic 19th century antique dating
from about 1845 so priced as an antique. Note the buyer's premium also.
I have several Dent Dipleidoscopes, including a rare Dent Universal
model capable of operating at times other than local solar noon and even
in the southern hemisphere. I gave a presentation on the Dent
Dipleidoscope at the Harvard conference of the North American Sundial
Society in 2013. If anyone is interested, I can provide a pdf of that
presentation. The presentation includes history, detailed explanation of
operation and lots of pictures of the construction of the dipleidoscope.
The Dent dipleidoscope provided an easy and inexpensive way to set
clocks at solar noon to an accuracy of better than tens of seconds, with
an achievable accuracy of about three seconds. Short of a noon transit
instrument at an observatory, it was the most accurate way to establish
time. Arguably, a hand-carried mechanical chronometer set that morning
at the Greenwich Observatory was also popular among bankers and
watchmakers in London, though it was a relatively expensive service.
But, the Dent Dipleidoscope could be used throughout England (and,
elsewhere) even on country estates. As the British trains began to run
with minute scheduling, accurate time became much more important!
Best of all, the Dent Dipleidoscope is astonishingly easy to use!
Larry McDavid
NASS Sundial Registrar
And, multiple HP Z3801A owner... times change!
--
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)
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