Mercury Artificial Horizon for Using a Sextant on Land

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Mercury Artificial Horizon for Using a Sextant on Land

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Sold Date: 12/10/2006
Channel: Online Auction
Source: eBay
Category: Fine Art

Artificial Horizon - 1870 - 1900

When using the techniques of celestial navigation in determining a position on land w a clear sea horizon is not visible an artificial horizon is absolutely necessary. The instrument is readied for use by placing the iron tray on a stable reasonably level surface and filling with mercury from the iron bottle using the iron funnel provided for the purpose; iron being the only inexpensive metal that will not amalgamate with mercury and turn into a paste. The glazed brass, roof shaped wind screen is then placed over the tray to keep the mercury surface still.

To take an altitude reading the navigator sights the celestial object directly in the usual manner with his sextant but instead of simultaneously sighting the sea horizon he sights the reflected image of the same celestial object from the mercury surface. The sextant reading is then divided by two to get the correct celestial altitude angle. Any older surveying or navigating book will explain the technique in greater detail if you are curious about it.

Interestingly, an artificial horizon similar to this one was among the few instruments taken by Lewis & Clark on their trans-continental expedition of 1803. The other instruments were: two sextants, a surveying compass and a marine chronometer . This was really all the "technology" they required for their position finding needs.

The instrument is housed in its fitted, hand dovetailed 8-1/2" X 6"X6" mahogany box with a typical British "trunk handle" on top and consists of an iron bottle of mercury, a screw stopper with leather gasket, a screw on iron funnel, a painted iron tray for the mercury and a glazed brass wind screen. The funnel fits the mercury bottle and the bottle closely fits its place in the box but the funnel does not screw into the iron tray the way the wood & ivory instruments do.

This instrument has no signature anyw on any part that I've been able to identify which is unusual for such a nice example of the instrument maker's art. The device, apart from a few spots of rust on the iron mercury tray; some "browning" on the mercury bottle & funnel; some normal age related scratches & chips to the varnish & paint work on the box, the wind screen and the mercury tray and some "dog earing" of the felt lining, is in very fine overall condition. The stain and residue on the box top could be easily to remove if the new owner wishes (but only if you know you want to keep it. See "guarantee below).

It should be noted that t are two symmetrical dents in the blackened brass wind screen w the mercury bottle has bumped it from the inside. The dents don't show in the pictures because they are rather slight and could be removed with the judicious application of a small light jeweler's hammer. (I try not to interfere with the ageing process if I can help it, fewer irrecoverable mistakes that way.)

Speaking of the dents, the instrument will be shipped triple boxed to avoid any more dents. That is, the mercury bottle will be packed securely in its own cardboard box along with a cardboard box containing the rest of the instrument (in its mahogany box) in a large peanut filled carton for the delivery guys to throw around. Yes the mercury bottle is brim full and could easily become "a loose cannon" in the instrument box if adequate precautions aren't taken. We will send the parcel "signed receipt required" so you and the delivery guy can both inspect the package when it arrives.

T is no reserve on this instrument. Someone is going to have a very merry Christmas with it. You CAN make it yours!!! Bid your limit the first time and don't risk getting "Snyped".

PAYMENT:

PAYMENT IS DUE AT THE END OF THE AUCTION! Ebay will send the winning bidder an email notification with payment instructions; just follow those instructions and send me the money within 7 days. (The quicker I get the money the quicker I can get your package off to you.) Otherwise I might assume that you are a "non paying" bidder and act accordingly.

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