Hallo friends,
I want to present you an interesting military chronometer:
Thomas Mercer, no 18965, Ministry of Defence Hydrographie Dept. H.S. 527-3635, Survey Chronometer regulated in sidereal time, with seconds contact and 24-hour indication, with lateral balance stop, seconds with window.
What is Sidereal Time:
As in observing a star, the earth takes 366 rotations to surround the sun, while the sun year has 365 days. So sidereal-time comes from the fact that the Earth makes a full rotation in its axis every 23 hours, 56 minutes and 3,5 seconds. Sidereal-time is used when determining a location’s exact coordinates on the Earth’s surface. It was for this purpose that this chronometer was regulated to sidereal-time.
(Btw, the crystal of this timepiece is broken, does anyone have a spare for me, maybe a complete but broken item??)
. Gruesse/Regards/Salute Konrad Knirim
PS: Have a look at my books on Military Timepieces:
. http://www.knirim.de

GREETINGS KONRAD, VERY INTERESTING PRESENTATION, ALSO A VERY GOOD EXPLANATION OF SIDEREAL TIME. EDDIE

quote:

Earth makes a full rotation in its axis every 23 hours, 56 minutes and 3,5 seconds.

not quite right...A sidereal day is approximately 23 hours, 56 minutes, 4.091 seconds
and a full rotation of the earth around the sun (revolution) is 365.26 days and not 366 days...

Thanks for sharing your photos of this exceptional timepiece. I would think that they did not make too many of them. Do you know the approximate age of this one? From the literature you have provided it shows two with serial numbers 15,032 and 15,421 were built for use in 1948. Since yours is serial number 18,965 my guess is much later?

Also, the literature says the winding is done 'through the glass' which sounds like the missing crystal should have a hole drilled in it over the winding stem through which the key is inserted without opening the front?

Should it have a battery inside, or is there an electrical connection for outside electricity to enter and then be regulated to control some outside mechanism?

Hallo Jimmy, you are right!
Hallo Jim, yes the glass has a whole for the key and one for the metal protection shown. My # 18965 is of 1950 (Tony Mercer, Chronometer Makers of the World)

Just in Ebay #260815221597 are 3 offered from Israeli submarine with issue plate, #26843 from 1969, text and photos:
This chronometer is one from 3 pices that supplied by the british admirality to the israeli navy in 1959, to be placed in the five british submarines that rebelt in portsmouth great britain and herewith ther story. On the 21st of September 1958 the government of Israel decided to purchase two submarines from Great Britain. They were 2nd World War "S " Class submarines, HMS Springer and HMS Sanguine. Both Submarines were build by Cammell Laird shipyards at Birkenhead during the war, and were launched towards the end of it.
A very scarce 2 Day mechanical marine chronometer by Thomas Mercer, St. Albans, England. No. 26843 is complete with baklite carrying case and leather strap. This chronometer is equipped with electrical contacts to operate slave units, a cutaway to the dial expose adjustment screws to make and break(half minute) contact points. Jewelled earnshaw type spring detent escapement, compensated balance and helical spring. Movement inscribed with serial number. Fully gimballed and in good working order, these sought after 2 days are becoming increadibly hard to find. Circa 1969.

Greetings Konrad

Wow, thank you for the "heads up" on the Israeli Chronometer, surely a very rare piece!

Regards

Out of curiosity, all the Mercer sidereal chronometers that I have seen have had the dial marked with a note indicating sidereal time, is there some other type of marking on yours that indicates that the movement is sidereal?

I see that the advertisement says this, but I also note that the dial has different markings.

Hallo Micheal, the back of the aluminum bowl is printed 'SIDEREAL TIME' (photo 2. row, 2. colum).
Amongst many other chronometer makers there were Hamilton M21 sidereal too!
Greetings Konrad Knirim

Hallo Friends,
see here documents showing that as well the Royal Navy as the Royal Air Force did use sidereal timepieces for navigation, mentioning here a RAF sidereal pocket watch 6B/51 and a RN sidereal stop watch H.S.7.
Greetings Konrad Knirim