The Nautical Sextant

A couple of weeks ago on e-bay I acquired a Heath vernier sextant for what seemed to be very little. When it arrived from Hawaii, it was plain that it had spent the evening of its life hanging on a wall, as a goodly amount of Hawaian dust and a bit of copper wire came with it. It was homeless too. Sextants without cases are much cheaper than those that still have them. I often wonder what becomes of the cases and spare telescopes and eye shades. I have only once managed to buy a sextant telescope (by Hughes and Son) and I have a beautifully constructed rosewood case that once housed a Heath Pillar Sextant. It seems that when a sextant is put on display, the case and its other contents get forgotten and then lost. Thus, my Hawaian sextant needed a new case and an inverting telescope, but first it had to be restored.

A previous owner seemed to have believed that sextants look better without their paint, especially if the frame appears to be made of brass (they are made of a high-tin bronze). All paint had been stripped, probably by dipping the instrument in a bath of paint remover, as it had even disappeared from the backs of the mirrors. Everything was encrusted in dust and fluff, and the silver arc and vernier scale were black with tarnish, but fortunately nothing was broken. From its construction, it was obviously by Heath and Company, but the placard on the index arm expansion which should have said ‘”HEZZANITH”,Endless Tangent Screw Automatic Clamp’ was missing.  As this device was patented in 1909 and Heath and Co merged with W S Stanley in 1926, shortly after which most sextants sold were micrometer instruments, I could date the orphan fairly well.

It seemed to breathe a sigh of relief as I carefully dismantled it down to the last screw and washer and cleaned each part individually in a soothing bath of 50% ammonia and dish-washing liquid. Screw heads had to have burrs removed and then be polished, moving parts degreased and paint applied where it would have been present in a brand new instrument. Usually, only the brass screw heads and the limb would be left unpainted, sometimes, too, the little protective covers for the mirror adjusting screws. Finally, it could be reassembled , with a smear of marine waterproof grease to moving parts, and the mirrors adjusted, with the result you see below.

It took some patience to get the lenses of the telescope clean of dust and dirt. I invariably dismantle telescopes down to their component parts. It makes it much easier to get at the optics and also gives an opportunity to lightly oil the very fine threads that hold the lens mount in place (I’m thinking of that next restorer in 50 years time). I had to make the body of the inverting telescope myself from scratch, turning it  from a length of 1 inch (25.4 mm) round brass bar. I have a selection of lenses from junked optical instruments. Half of a pair of early 6 x 22 mm binoculars provided the lenses for this scope. I had to make a new eyepiece  and fit it to a length of 3/4 inch (19.05 mm) brass tube for a draw tube. It works well and there is no tell-tale blooming of the lenses to indicate that they are post-1950.

The case is made from my precious supply of solid African mahogany. A case of this period would have had comb joints at the corners, but these need special machinery to make, so I used box dovetails appropriate to the period. Pre-1900 cases usually had dovetailed corners, but with very fine pins (the bits that fit between the tails). I haven’t yet learned how to make these successfully, and in any case, they would be out of period. I carved the hook latches out of brass, using one from a Hughes and Son case as a template. The handle would have been of cast brass. Ones of the correct pattern are hard to find and expensive, so I am waiting for my income tax refund before stocking up on a few and buying some silver nitrate to use in re-silvering the mirrors.

You will find more about restoring in my book.