Scientific instruments such as compasses, microscopes, sextants and dialling spheres can be worth from hundreds of pounds to five-figure sums in the auction houses.
Mr Peter Bateman of Edward Butler Antiques, Bachelor's Walk, Dublin, says octants (an eighth of a circle) and the more accurate sextants (a sixth of a circle), used to determine one's location on the globe, can vary in value from £400 (€508) "up to the thousands".
Chronometers - very accurate timekeepers used on board ships - can also be valuable. These are clocks on a gimbal system in a box, which ensures the clocks stay level even when the ship is tilting. Chronometers also help determine a ship's position at sea.
"They're always expensive and at the bottom end of the scale you're probably talking about £800 and they go up into the thousands again depending on makers and all that," he says.
Old microscopes are always a favourite with collectors. "The early ones again are very popular and are usually made out of brass. If you get the microscope, it's very often in a fitted box with different lenses of different magnification and extra bits and pieces to go with it. Some people discover them in their attics from the past. Certainly £200 would be the bottom one there and again up to the thousands for very special makers."
Handheld compasses dating from the Georgian era can be worth around £300, while military compasses from the first and second World Wars can still be picked up for under £100. "And they're quite nice instruments," he says.
Telescopes are also popular. "It's important for anybody buying these things or establishing their value that there aren't pieces missing out of them. Anything of that age that's defective, it devalues them in a big way.
"And for people who would be investing in them, one of the first things to look for is that they're complete and all there. Otherwise, you're buying trouble. It's hard to find, and costly to get, bits and pieces that are original."
Mr Tom Newth is a specialist in the scientific instruments department at Christie's in London, which has an auction of scientific and engineering works of art on April 13th.
He advises collectors to avoid instruments that are very brightly polished. Either they have been over-cleaned or they are a modern reproduction, "neither of which is good. Obviously it's better if it's an older piece that's been cleaned, but that vastly depreciates the value".
So, should people with a scientific instrument that they suspect might be valuable avoid cleaning it? "Exactly, yes. I mean if something is really dirty, it's normally advisable to clean it gently but never polish, for example, a lacquered brass instrument under any circumstances."
Names to look out for are "legion" but a look through auction catalogues to see which ones appear to command higher prices than others on similar pieces can give a clue to value. Workmanship will certainly also add value. Other than that, obviously age, as with all antiques, tends to add value, he says.
An example of an exquisite engraving commanding high values is a mid-17th century French copper and brass religious icon with sundials in the forthcoming auction, estimated at £30,000-£40,000 sterling (€49,000-€65,000). A late 17th century brass astronomical dialling sphere used for navigation or in the construction of simpler navigational instruments is estimated at £40,000-£60,000 sterling. And a rare quarter-inch long fragment of meteorite believed to be Martian which fell in Nigeria in 1962 and verified as Martian by scientists from the University of California in 1995 is estimated at £2,000-£3,000.
jmarms@irish-times.ie
