[time-nuts] Setting Clocks in the Mid 1800's

Larry McDavid lmcdavid at lmceng.com
Fri Oct 31 23:23:05 EDT 2014

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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