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I think the main virtue of an ivory scale was its clarity of reading.
Take a look at some of the ivory-scale instruments in "Taking the
stars". It was far better, in an octant, than the original boxwood, in
which the inherent grain tended to deflect the engraver's tool, ever
so slightly. Ivory had no such grain, and could take a really fine
engraved line, which with a bit of lamp-black rubbed in, created a
beautiful contrast with the bright white surface.

As for whether it matched the expansion of the ebony it faced, I doubt
it, to judge by many old museum instruments, in which small cracks can
be seen in the ivory inlay.

I don't think it can have been nearly as expensive as Alex makes out.
Before the days of plastic, all the keys of a piano (even a cottage
upright) were faced with ivory, and so were billiard- and snooker
balls. It was imported in large quantities, and there was an enormous
warehouse (Ivory House, at St Katherine's Dock, near the Tower of
London) to handle it.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


----- Original Message -----
From: "alex" 
To: "NavList" 
Sent: Monday, January 08, 2007 12:15 AM
Subject: [NavList 1996] ivory scales


|
| Why the scales of octants and some sextants
| were made of ivory?
| Does ivory have some favorable heat expansion properties?
| Or any other good physical properties?
| Or what? If I understand correctly that "ivory" is the substance
| made of an elefant's tusk,
| it seems to be that even in 1820-s ivory was not cheaper
| than silver. I could not figure the price, but only found
| that 3,000 cwt (=hindredweight=100 pounds) of ivory
| was sold in 1827 in London.
| I'd guess that silver was cheaper.
|
| On the other hands ivory was used on cheap octants
| and silver (or gold or platina) on expensive sextants.
|
| (Nowadays it is reversed, of course: cheap American
| ebony-ivory-brass octants
| are sold on e-bay for higher price than fancy British sextants:-)
|
| Alex.
|
|
| |
|


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