A French Hydrographic Sextant

13 01 2019
2 a case inside

Figure 1: Sextant in its case.

I recently acquired for a relatively modest sum the three-circle vernier sextant shown in Figure 1. Attached at the front corner of the frame is a plate engraved with the letters “S.H.” or “Service Hydrographique (de la Marine)” or French Naval Hydrographical Service, formed in 1886 as successor to the “Dépôt des cartes et plans de la Marine”, founded in 1720. The plate seems to serve no other purpose that I can think of  than as an identifier.

3 a e bouty name

Figure 2: Front of the tangent screw mechanism.

Engraved on the front of the tangent screw mechanism is the name “E. Bouty”. Edmond Bouty (1845 – 1922) was a physicist in the Science Faculty at Paris, but I cannot find that he was an instrument maker, nor is there any other name on the sextant. It may be that his contribution was the design of the scale lighting system, about which more later. It is not even clear that the sextant is of  French manufacture, as at the left end of the limb are the letters “D.S.” indicating Deutsche Seewarte, the German Hydrographical Service, but the frame, of about 180 mm radius, differs in detail from that of C Plath’s Dreikreis sextant.

2 b frame turning marks

Figure 3: Turning marks on front of frame.

The bronze frame is of no particular interest except that when clearing old and perished paint from the frame during restoration I noticed marks (Figure 3) that showed that it had been faced in a lathe, giving a small clue to the manufacturing process.

3 c spring nut

Figure 4: Spring box detail.

Returning to the tangent screw mechanism, the spring box is shown exploded in Figure 4. A tongue on the sliding block is trapped between the end of the tangent screw and a long spring mounted on a guide and retained by a nut. The end of the guide can be seen on the right of Figure 2.

3 b clamp

Figure 5: Exploded view of index arm clamp.

The sliding block is retained in its slide in the lower end of the index arm by the retaining spring on the upper right of Figure 5, while the clamp screw and its leaf spring bears on the back of the limb. In use, the clamp is slackened and the index arm moved approximately into position, when the clamp is tightened, thus fixing the sliding block to the limb. Turning the tangent screw thus moves the index arm about the sliding block against the pre-load of the helical spring as a means of fine adjustment. In truth, it is the index arm that slides rather than the sliding block, but as no one else had given it a name, I decided to do so when writing “The Nautical Sextant.” This system of applying pre-load was used in many vernier instruments such as vernier theodolites and gun aiming systems. as well as in several makes of sextant.

4 perp adjust

Figure 6: Index mirror bracket.

The index mirror is held against a vertical bracket by means of a clip which is tightened against the bracket by means of a screw bearing on the back of the bracket. The mirror is made perpendicular to the arc of the sextant by a system that seems  to have been used only by French makers. Two screws attach the radiused feet of the bracket to the upper end of the index arm and the end of a screw held captive in the base of the bracket can then rock the bracket to bring the mirror square to the plane of the arc..

5 side error

Figure 7: Horizon mirror bracket.

Figure 7 shows a somewhat similar method of adjusting out side error of the horizon mirror, but in this case a deep slot cut nearly through the base of the bracket gives flexibility to the the adjustment by means of another captive screw.

7 horizon mirror

Figure 8: Horizon mirror detail.

The detail shown in Figure 8, as well as making clearer how the mirrors are held against their brackets, shows that the horizon mirror bracket can be adjustably rotated about an axis vertical to the plane of the sextant, in order to adjust out index error. Note that the mirror is fully silvered, which means that the direct view of the horizon does not pass through glass and that the edge of the silvering of the mirror can be given better protection against corrosion. It does however result in a smaller area of overlap of the direct image of the horizon and the  reflected  image of the observed body when using a Galilean telescope. Enter “Freiberger yacht sextant” in the search box at the top of the page for a discussion of why this is so.

6 index error

Figure 9: Detail of index error adjustment.

Figure 9 gives more detail on the index error adjustment. There is a boss as an axis on the underside of the horizon mirror bracket that passes through the frame and is held by a retaining screw. A further boss passes through a clearance hole in the frame  and has an internal thread tapped in it as a nut. The index error adjusting screw, held captive in the frame by a screw and clamp, engages with the “nut”, so that when the adjusting screw is turned, the whole mirror bracket rotates. When adjustment is complete, the bracket is locked in place by a  clamp screw..

This is a rather complex means of adjustment of the horizon mirror, which had long been achieved much more simply by means of   a pair of screws bearing against the back of the mirror, while lugs on the mirror clamp provided spring loading. Elegant though it may have seemed to its (?) French inventor, it is unnecessarily complex., though perhaps no more complex than the solution adopted by Brandis and its US successors.

9 battery handle

Figure 10: Interior of battery handle.

This sextant represents perhaps one of the earliest ones to light the scale in poor light. Scale lighting had to wait for the development of suitable dry batteries in the 1890s and of miniature flashlight bulbs with robust tungsten filaments in about 1904.

Figure 9 shows the interior of the Bakelite handle which accepts a 3 volt 2R10 battery.  A screw at the lower end holds the negative pole of the battery firmly in electrical contact with the frame of the sextant and at the upper end a spring loaded switch plunger makes contact with the positive pole. The top end of the lid is bevelled and the lid itself is slightly bowed, so that when rotated closed it remains in place.

10 b handle to bearing

Figure 11: Wire from handle to foot.

A wire passes from the body of the switch to the foot (Figure 11), inside which is a spring loaded brass plunger (Figure 12).

10 a switch to contact

Figure 12: Inside of foot.

The index arm journal is hollow and a wire passes up its centre to an insulated contact on the end, to make electrical contact with the contact inside the foot (Figure 13).

11 a journal contact

Figure 13: Insulated index arm contact.

The other end of the insulated wire passes down the index arm in a machined groove to a clip held on an insulator block (Figure 14).

12 lighting system

Figure 14: Lighting bulb holder.

The clip makes contact with the outside of the bulb holder and thence to the central contact on the bulb. The outside of the holder is insulated from the brass interior, which is threaded for the bulb. The brass interior fits snugly in the cylindrical shade which is attached to the index arm and hence the frame, thus completing the electrical circuit. Most subsequent makers contented themselves with a simple loop of insulated wire to conduct electricity to the bulb, but this more complex and no doubt more expensive system has the merit of not flexing any wire. Like most complex systems, however, there is more to go wrong.

13 rising piece in situ

Figure 15: Rising piece.

The telescope rising piece (Figure 15) is simpler than that of many of its early 20th century competitors and it has a rectangular mortice machined in its face to engage closely with a tenon on the telescope bracket, so that it can be slid up or down to vary the amount of light from the horizon entering the telescope. Collimation is standard, by means of a tilting telescope ring held in place by two screws.

8 index shades

Figure 16: Shades mounting.

The shades make none of the usual provisions to prevent movement of one being transmitted to its neighbours. Resistance to rotation is given by means of a Belleville washer, a conical washer with the characteristics of a short, stiff spring. Since these date from about 1870, they add no clues to the age of this sextant.

15 telescopes

Figure 17: Telescope kit.

The kit of telescopes shown in Figure 16 is for the most part standard, with a 4 x 24 mm Galilean “star” telescope for general use and a 6 x 16mm Keplerian “inverting”  telescope. By the twentieth century, this latter probably received little use except for artificial horizon sights to rate chronometers in out-of-the-way places of known longitude. The large 3 x 36mm Keplerian telescope is of interest as it has a wide angle eyepiece with an eye lens of 25 mm aperture. This gives an image nearly as bright as the 4 x 24mm telescope (the extra lens in the eyepiece causes some loss of light) and with a field of view about four to five times wider.

1 a case exterior

Figure 17: Case exterior.

The mahogany case was much battered and stained, and with several shrinkage cracks, so it was gratifying to be able to restore it to the state shown in Figure 17. It looks decidedly English and placing the handle on the side follows Henry Hughes and Son’s practice, but neither the sextant frame nor the mirror mountings  are consistent with this.

If you enjoyed reading about this sextant, you may also enjoy reading my “The Mariner’s Chronometer“, also available via Amazon.com.





A later Shackman sextant: a guest blog post.

14 03 2018

John Triplett recently wrote to me about a Shackman sextant that he had acquired and kindly agreed to write a guest blog post. In what follows, comments that I make are shown in blue.

It wasn’t very long after I first read Bill’s blog entry on Shackman sextants (https://sextantbook.com/category/shackman-sextant-and-link-to-ramsden/) that I had the opportunity to acquire one, and at an extremely reasonable price.  I found the design to be unique and interesting, and wanted to see it up close.  I found this sextant in a recent eBay auction that was listed referencing its reseller, Kelvin & Wilfrid O. White of Boston, and not its maker, D. Shackman & Sons (Figure 1).


Figure 1: The sextant sitting on its case.

In making some needed repairs (the index arm was bent away from the limb and had to be straightened), it soon became apparent that there are some design differences between Bill’s sextant and mine.  My sextant has a later serial number (No. 3236) than Bill’s (No. 2262), and that does seem speak to some of the differences between the two pieces.  As of this writing, there is another Shackman sextant being offered on eBay (again, resold by Kelvin & Wilfrid O. White) with a serial number (No. 2097) even lower than Bill’s, and having characteristics of Bill’s earlier number, specifically the short tail and leaf spring on the index.    No. 2097 also has a 30” micrometer with a single index line, not a 10” micrometer with a vernier, so, either different precisions were made by Shackman, perhaps some for survey purposes and others for higher precision needs in navigation, or the more precise vernier was a later revision. Most non-British makers had by this time begun to abandon the vernier, perhaps recognising that errors due to uncertainty about the dip of the horizon tend to swamp instrumental errors, which in any case are sometimes of the order of 30 seconds. If greater precision is needed, it is easy to estimate to 0,2 degrees, but such precision is likely to be devoid of meaning, given that the instruments were calibrated at only 30, 60, 90 and 120 degrees.

It generally appeared to be in fine condition, very clean, and showing very little use.  As for the needed repairs, my best guess is that this sextant was dropped early in its career at the US Merchant Marine Academy (as the property label on the box suggests), and, once the owners discovered the nature of the damage, it was simply shelved and forgotten.  (This long convalescence is further evidenced by the light damage to the lid of the box:  papers left on the top for a long period resulted in a stark bleaching/darkening pattern from a masked exposure (See Fig 1.)  Some disassembly was required, and this process uncovered some of the aforementioned differences.

The noted differences to my No. 3236 are:

  • ‘Paddle’ or ‘spoon’ grip extensions on the index and worm that improve manipulation and placement of the micrometer movement. One of the ‘spoons’ is deformed from the drop impact. See Figure 2 for close up view.
  • Copy of IMG_3295_preview

    Figure 2: Damage to release catch “paddle”.

  • The leaf spring has been replaced with a coil spring and plunger system that applies and maintains the pressure of the worm against the rack. The spring slides in and bears on a curved groove on the underside of the opposite paddle grip (Figure 3).
  • Copy of IMG_3294_preview

    Figure 3: Radial helical pre-load spring.

  • The index journal bearing system has seen a design change from the keyed washer to a spring and washer. (This was discovered when the index arm was removed from the frame for repair.) This is such a strange arrangement that I think it must be a later and rather clumsy repair. The washer under the head of the screw does not seem to have a square hole, so there is nothing to stop the washer from working the screw loose as the latter rotates with the journal (Figure 4).
  • Resulting in part from some of the above changes, the later sextant is positioned differently in the case to allow room for the elongated worm assembly.

Ironically, the strength of the ribbed arm casting Bill references in his original blog either worked well or not at all, depending on how you look at it.  It certainly preserved the alignment of the ribbed section of the arm, but fully transferred the bending moment into the weakest part of the arm at the hole for the journal mount.  In agreement with Bill’s assessment, this inherent weakness certainly makes the arm rib a questionable design point, and an overkill in manufacturing.

As for the spring-and-plunger system, this could be considered the Achilles’ Heel of this design.  The spring seems, to me, to be undersized and understrength. Once the spring becomes weakened to a critical point, there is no longer sufficient pressure to keep the worm against the rack; the user has to consciously add the needed force by hand. (Perhaps this too was a later repair. The spring seen in Figure 3 should perhaps be a larger one that fits outside the fitting in which the foot of the spring presently sits.)  It is especially annoying in that it occurs mostly when you are trying to use it normally.  The worm tends to fall away from the rack rather than onto it as does, say, a Hezzanith Endless Tangent Screw.  When turned ‘backwards’, the worm tends to ‘bite’ the rack and assist the spring in holding against it; when turned ‘forward’, the worm throws itself away from the rack and works against the spring.  This tendency was especially pronounced when I first received the sextant and the rack and worm were dry.  After the repair, a proper oiling to the contacting parts greatly mitigated this effect, but it is still noticeable

Another observation on an avoidable issue is the cork padding on the case top braces that contact the ends of the limb and the scope.  In addition to being glued down, they are actually nailed in place.  My example has some shoddy factory work in this aspect as one nailed head was bent over, leaving the edge higher than the cork.  The bronze surface at the left end of the limb is fairly mangled up from years of contact.  Was this really necessary?  Simply gluing it would have been just as effective and far more maintenance friendly for replacement.  Happily, the DS&S logo on the other end has fared much better. Shackman’s were manufacturing jewellers pre-war and probably did not make the case. It may well be that more careful woodworkers were doing war work deemed to be more important, e.g. making the all-wood Mospquito aircraft.


Figure 4: Shoddy workmanship.

The Shackman sextant is, aesthetically, a very attractive piece.  The simple and elegant all-black frame is highlighted only by the bronze of the limb and truly tangent micrometer (and maybe some exposed scope slide), which, while giving a striking appearance, is also quite functional and uniform for usage – the eye is naturally drawn to the scales that need to be read, and in somewhat of a progressive manner.  Also, for a non-engineering, non-optical firm, Shackman’s optics are very good (although they could have been subcontracted).  The telescope is very bright and clear, noticeably more so than those of my instrument by Buff & Buff, a maker known for excellent optics.  It is not a perfect design, as Bill points out, and suffers from some over complexity and confusing ideas that needlessly reduce its functionality in other ways and, quite possibly, its accuracy.  While the solid bronze casting is strong and rigid, its significant weight is felt rather quickly when trying to make an observation.  Still, I find it to be, overall, a rare, unique, and lovely design that makes for a desirable addition to a collection, and I am enjoying becoming more familiar with it.

Thank you, John.


Hughes and Son Admiralty pattern micrometer sextant

14 02 2018

I wrote about a Hughes and Son Admiralty pattern vernier sextant on 23rd June 2011, concentrating on its telescopes, its rising piece for the latter and its sealed mirrors. Recently, I acquired an Admiralty pattern micrometer sextant, probably part of a batch ordered in the closing days of WWII. The main difference is in the micrometer mechanism while the index arm bearing, mirrors, shades and telescopes are essentially the same as in the vernier sextant, certified in March of 1939, so I will not cover that ground again. Figure 1 shows the instrument as advertised by the seller, who seems to have photographed it through a light green filter. This explains the green cast to the blue-grey paint (I have removed the bright green background).

As bought

Figure 1: As bought.

The sextant was in a rather grubby condition, with paint beginning to perish and flake off in parts. I suspect it had been well-used, rather than spending nearly all its life in a cupboard.

Figure 2 shows the front view after a complete strip-down and restoration. In it I have labelled the main parts of a micrometer section for the benefit of newcomers to my site, and those who may not yet have purchased my book “The Nautical Sextant”, which looks in great detail at the structure of these instruments.

A 1 GA front

Figure 2: Front view of restored sextant.

Figure 3 shows the rear (or right hand side when in use). Here it is possible to see why this sextant, weighing in at 2.05 kg (4.52 lb) is so heavy. The cast bronze frame is very heavily ribbed compared to most other sextants, and features like the rising piece, the Index arm bearing cover and the complex arrangements for sealing the mirrors have all added to the weight. Earlier Hughes and Son instruments with scale lighting made the battery handle out of wood, but this one is of molded Bakelite with a brass battery cover. Happily, it contained no batteries nor signs of corrosion.

A2 GA back

Figure 3: Rear view of restored sextant.

Figure 4 shows details of the micrometer mechanism. The worm engages with the rack, which is cut into the edge of the limb. The rack is in essence a segment of a worm wheel having 720 teeth. Also cut into the edge of the limb is a groove which accepts the free edge of the two keepers. These prevent the index arm from lifting off the limb.

A3 micrometer detail

Figure 4: Details of micrometer mechanism.

The axial pre-load spring, which is shown out of place, is U-shaped with one upright of the U being forked to embrace the worm shaft and press on the flange immediately to the left of the thrust bearing. The worm shaft inside the bearing is conical, so it aligns the shaft axially and radially with a further bearing providing more radial guidance. This spring is a simpler solution to providing thrust pre-load than the more complicated systems used by Hughes and other makers prior to WW II.

The worm is held in engagement with the rack by a beryllium-copper radial pre-load spring. A simple cam bears on an arm extending from the swing arm on which the bearings and worm are mounted. When the release catch is operated, the cam causes the swing arm to rotate around a substantial bearing  and the worm disengages so that the index arm can be swung rapidly to a new position. When the release catch is let go, the spring swings the worm back into engagement with the rack and rotation of the micrometer drum provides fine adjustment.

There is a guard extending from the swing arm to provide some protection to the micrometer drum and the worm shaft. The shaft is often bent when a sextant is dropped or knocked and, as replacement parts have long been unobtainable, a whole worm and shaft have to be made. See for example “A Worm Turns” on this site on 23rd June 2011. The worm itself receives some protection from a sheet metal cover, seen in Figure 3.

Figure 4 shows the front of the index arm in the area of the worm. The screw that secures the axis about which the swing arm rotates has been removed to show a washer that is prevented from rotating by two pins into the swing arm, so that the screw can be adjusted to remove end shake in the bearing, while preventing movement of the swing arm from loosening or tightening the screw.

A4 micrometer front

Figure 5: More micrometer details.

There seems to be little point in providing a vernier to the micrometer, as the racks of this era often had errors in excess of 0.5 minutes and in any case, observation errors due to uncertainties about refraction and dip would often swamp instrument errors. Most makers after WWII abandoned micrometer verniers, but some were still made, presumably to satisfy conservative mariners and military procurement officers.

This instrument was provided with a fairly comprehensive kit of telescope and tools, shown in Figure 6.  Most mariners probably never used anything other than the Galilean (“star”) telescopes in the 20th century.  The higher powered ones were probably used mainly for artificial horizon shots in ports of known longitude to correct chronometers. This was made obsolete by the advent of radio time signals, but Tamaya in particular continued to provide them to the very end of sextant manufacture.

A6 telescopes etc

Figure 7: Ancillaries.

The eyepiece shades are useful for finding the index or zero error of the sextant by looking at the sun or moon, but again, most mariners would simply have used combinations of horizon and index shades, or used the horizon to avoid strain on the neck from looking up at the sun.

A very useful feature of the Galilean telescopes is the provision of hoods to prevent glare from around the horizon mirror reaching the eye, as the hood limits the field of view to the mirror alone (Figure 8).

A5 telescope hood

Figure 8: Telescope hood.

Figure 9 shows the sextant and its telescopes etc. in its fine mahogany case. As usual from about 1900 onwards, the corners have box comb joints. In all Hughes and Son sextants, the handle is on the right hand side, to avoid setting down the box on its hinges.

A7 in box

Figure 9: The sextant in its case.

Figure 10, shows the case standing on its left hand side. This, together with the hook latches which always face to the left, so that they tend to remain latched in the carrying position, identifies the sextant as a Hughes and Son, if it were not obvious from the circular “Husun” emblem attached to the index arm.

A8 latches

Figure 10: Hook latches in closed position.

If you have enjoyed reading this account, you will find much more of the same in my book “The Nautical Sextant”, but do not expect to find anything about in it about navigation. It is about the structure of the sextant.You can find plenty of positive reviews of the book on the amazon.com web site.




6 03 2010


 As the pages of the blog posts are not numbered, I have given the dates of the index entries as the easiest way of retrieving the information they contain. Don’t forget that WordPress also allows you to search this site specifically (see search box in top right-hand corner of the home page).

adhesives, industrial       27 Mar 11

Admiralty, British, vernier pattern of sextant     27 Mar 11,  24 June 11

Admiralty, British, micrometer version of sextant    15 Feb, 18

alcohol, filling of A10 A bubble chambers   13 Oct 09

angle, vertical sextant     13 Jul 12

Araldite, for cementing lenses       24 Jan 10

refractive index of                    24 Jan 10 (Comment)

arc, dangers of polishing                                    24 Jan 10

platinum                                                           10 June 10

silver, letting in to limb                               10 June 10

astigmatiser shade             20 Mar 11

autocollimator, principle of                                6 July 09, 13 Feb 11

accuracy of                     12 Mar 09,  13 Feb 11

calibrating dip meter with             5 Apr 2012

setting wires of                13 Feb11

view through eyepiece of      13 Feb 11

backlash     12 Mar 09

beam splitter     13 Feb11


index arm           18 Feb 10, 13 Jul 12

adjusting     12 Mar 09

of US Maritime Commission sextant    15 Dec 10

swing arm

conical centres     12 Mar 09

plain     12 Mar 09

of US Maritime Commission sextant     15 Dec 10

Belleville washer                                               18 Feb 10, 11 Aug 09

Blish prism                                                      5 Apr 2012

Bracket, mirror,

bent     20 Oct 16

slotted                1 Oct 14

shade                                14 June15

brass, hammered                                              10 Nov 09

bubble chamber

overhaul, of AN5851                            20 Dec 08

refilling, of AN5851     20 Dec 08

bubble sextant

A  Coutinho  Pattern                   6 May 16


A10 series                                            25 Feb 09, 13  Oct 10

screw closure of     13 Oct 10

Mk IX series                                        25 Feb 09

British Admiralty pattern sextant      24 June 11

Broken legs, mending  7 Oct 16

Byrd sextant                                                     30 May 09

Byrd, Commander Richard                               30 May 09

calibration, of C18 sextant                        10 June 10

calibrator, sextant

calibration of           13 Feb11

construction of        13 Feb 11

mounting sextant on    13 Feb 11

Carbonara, Victor             1 Oct 14

Carl Path’s earliest sextant (see also C Plath)       21 April 2017


latches                                                      18 Feb 10

keystone                                                  17 Dec 09

furniture, of US Maritime Commission sextant  15 Dec 10

plywood, delamination of                           14 June 15

casting, pressure die-                                     14 July10

C Plath (See also Carl Plath and Plath)

production numbers       14 July 10 (see also Plath)

sextants, eighty years of     13 Nov 12

yachting sextant                    14 June 15

centres, as bearings     12 Mar 09

chassis, swing arm     12 Mar 09

of La Filotecnica sextant 5 Oct 10

CHO-M sextant. See SNO-M sextant

Chronometer, marine    See www.chronometerbook.com

cleaning sextant parts             18 Feb 10, 23 Nov 08

clearance, axial of worm     12 Mar 09

collimating rising piece     2 September 11

collimation, faulty     2 September 11

collimator      13 Deb 11

horizontal     13 Feb 11

Commission, US Maritime   15 Dec 10

Cooke and Son                       28 Apr 10

Coutinho Pattern Bubble sextant   6 May 16

Dip                                        5 Apr 2012

abnormal                  5 Apr 2012

meters                       5 Apr 2012, 23 June 2012

calibration of             5 Apr 2012

Dollond, John                           10 June 10

Dollond, Peter                           10 June 10

double sextant                                                  16 Jul

micrometer mechanism of                     16 Jul 09

handle of                                              16 Jul 09

mirrors of                                             16 Jul 09

optical paths of                         16 Jul 09

telescope of                                          16 Jul 09

distance meter,

Fiske     13 Nov 12

Fleuriais     4 Nov 12

Stuart      13 Nov 12, 13 July 12

drawings, of SNO-T mirror adjusting screw and bush 17 april 10

drill, slot, use of  17 April 10

error, index, adjustment            1 Oct 14

side, adjustment            1 Oct 14

perpendicularity, adjustment            1 Oct 14

errors, of worm     12 Mar 09

Entandrophragma cylindricum, see sapele


micrometer                                           22 Mar 09

monocular, disassembly                        18 Nov 09

positioning                                18 Nov 09

of C Plath’s earliest sextant          April 21 2017

fake C Plath sextants                   14 July 10

La Filotecnica Salmoiraghi        5 Oct 10

Filby, David      13 Nov 12, 21 April 2017

float glasss                                                        11 Feb 09

Florez, Luis de                                      30 May 09

Francis Barker ,sextant, small craft precision     14 June 15


        aluminium alloy          29 Sept 10, 13 Nov 12, 14 June 15

        bent     20 Mar 11

braced                                                            10 June 10

bronze                    29 Sept 10, 13 Nov 12

         curve bar pattern      28 Jan 10

          Dreikreis                                             24 Jan 10

of C Plath’s earliest sextant    21 April 2017

evolution of                                        29 Sept 10

of Freiberger Skalensextant                                   22 Mar 09

of La Fil0tecnica               5 Oct 10

plastic                                                      29 Sept 10

pressure die cast                                  26 Oct 08,  29 Sept 10

stiffness of Heath sextant                      28 Jan 10

of Plath sextant                        28 Jan 10, 14 June 15

                      of  tulip pattern                                                10 Nov 09

of US Maritime Commission sextant  15 Dec 10

Freiberger , yacht sextant              14 June 15, 10 Aug 11,

skalen sextant 4 Apr 10

drum sextant   22 Mar 09

Gavrisheff dip meter                                         5 Apr 2012

Gilbert and Company                                      10 June 10

glass, float                                                        11 Feb 09, 27 Jan 09

graduations, sextant, refilling                              18 Nov 09

grinding paste, for circular mirror     27 Mar 11

Hall, Chester Moor                                                    10 June 10


detachable            1 Oct 14

kinematic mounting of       20 Mar 11

of double sextant     16 July 09

of Gilbert sextant   10 June 10

of La Filotecnica sextant 5 Oct 10

of Troughton and Simms sextant   28 April 10

of US Maritime commission sextant  15 Dec 10

of WWII C Plath sextant                     14 July 10

Heath curve bar sextant,

frame stiffness                          28 Jan 10

tangent screw                                      28 Jan 10


micrometer shaft bearings                      24 May 09, 5 May 09

rack                                                     24 May 09

swing arm bearings                               5 May 09

vernier sextant                                      23 Nov 08


Admiralty pattern sextant, vernier    27 Mar 11,  24 June 11

micrometer    14 Feb 18

lamp switch assembly                            18 Feb 10

micrometer mechanism              18 Feb 10, 18 Feb 18

rack                                                     3 Jan 09

telescope mounting                               18 Feb 10

index arm

Ilon Industries Mark III sextant            1 Oct  14           14 Jun 15

index arm, bearing                             18 Feb 10, 22 Nov 08, 14 June 15

C Plath                                          14 July 10, 13 Nov 12, 14 June 15

SNO-M                                           14 July 10

US Maritime Commission    15 Dec 10

index mirror turntable                                10 June 10

sealed     24 June11, 14 Jun 15

joint, corner rebate                                           11 Aug 09

Keeper, index arm                 14 June 15

, swing arm                14 June 15

lacquer, see paint

lamp assembly, making new for Husun  18 Feb 10

latches, of case                                     18 Feb 10, 24 June 11

left-handed sextant                                            2 Dec 08


broken, mending                           7 Oct 16

turning new                                           24 Jan 10

placement of                                         6 May 09, 26 Apr 09, 2 Dec 08


auxiliary                                                30 May 09

recementing                                          24 Jan 10

swaging                                                24 Jan 10

achromatic, airspaced                   10 June 10

Leupold and Stevens see US Maritime Commission sextant, 15 Dec 10

level, spirit                                                        30 May 09

sensitivity of                                          30 May 09

light path, in Ilon Mark III sextant              1 Oct 14

lighting, of scale                                                30 May 09

limb, rivetted to frame                                  10 June 10

chromium plated                  5 Oct 10

logo, probable fake Plath                              14 July 10

of La Filotecnica Salmoirhagi       5  Oct 10

lost motion    See backlash

makers names                                                   10 Nov 09

mandrel, test     20 Mar 11

meter, dip, an improvised                 5 Apr 2012

Gavrisheff                                5 Apr 2012

Russian naval                        23 Jun 2012


eyepiece                                         22 Mar 09, 13 Feb 11


bearing, by C Plath     20 Mar 11

bent         20 Mar 11

calibration of                                         6 July 09

drum, making new, dividing       20 Mar 11

numbering       20 Mar 11

evolution of                                           3 Jan 09

examination of                          6 July 09

index, bent          20 Oct 16

mechanism                          18 Feb 10, 14 June 15

of  Husun                                   3 Jan 09

of Ilon Industries Mark III            1 Oct 14

by Carl Plath                            3 Jan 09, 13 Nov 12

shaft, bearings,  by Heath                        24 May 09, 5 May 09

bent, repair of     20 Oct 16

by La Filotecnica     5 Oct 10

by C Plath     20 Mar 11

setting errors of     13 Feb 1

of US Maritime Commission sextant 15 Dec 10

version of Admiralty pattern sextant   15 Feb 18

worm, axial play in       14 June 15

Micrometre a reflexion, Fleuriais’     4 Nov 12


adjusting screws, of SNO-T    17 April 10

auxiliary                                     30 May 09

backing of brass sheet,  15 Dec 10

blank, preparation of circular     27 Mar 11

bracket, Ilon Mark III sextant            1 Oct 14

bracket, SNO-T, repair of     17 April 10

Observator, repair of     20 Oct 16

bracket, C Plath casting numbers   14 July 10

circular, cutting       27 Mar 11

first surface            1 Oct 14

f latness of                                             27 Jan 09

grinding  edges                          11 Feb 09

horizon, C19 mounting assembly           10 Nov 09

Gilbert method of adjusting     10 June 10

Overcoated    13 Nov 12

Plath and SNO-M  compared  14 July 10

sealed  24 June11

index,              of Troughton and Simms sextant    28 April 10

,         , adjustment   14 June 15

adjustment by turntable      10 June 10

making new                                          11 Feb 09

removing silvering from             11 Feb 09

rounding corners                                   11 Feb 09

sealed                                                   6 May 09,  24 June 11

Mk IX A sextant restoration manual                  17 Nov 08

magnifier, scale, mounting in vernier sextant   24 June 11


eyepiece disassembly                           18 Nov 09

labyrinth seal of objective lens      20 Mar 11

La Filotecnica                     5 Oct 10

mounting,                                             18 Nov 09

Freiberger, boring                      18 Nov 09

marking out                  18 Nov

milling and shaping        18 Nov 09

squareness                                18 Nov 09

prismatic, in Ilon sextant            1 Oct 14

prismatic, making                                  18 Nov 09

removing objective                                18 Nov 09

removing prisms                                    18 Nov 09

separating halves                                  18 Nov 09

Tamaya etc                                           28 Jan 09

mounting, of Husun telescope                            18 Feb 10

of La Filotecnica telescopes     5 Oct 10

Navistar professional sextant     13 Nov 12

objective, removing from monocular                  18 Nov 09

octant, aeronautical, Mark I Mod 3                   2 Dec 08

O rings, Viton  13 Oct 10

Neoprene 13 Oct 10


defective    15 Dec 10

for sextant finishing                                   24 Jan 10,10 Nov 09

photoluminescent                                  9 Dec 08, 26 Oct 08

wrinkle finish                                         18 Feb 10

Parallax, solar     4 Nov 12


Dreikreis sextant                          24 Jan 10, 13 Nov 12

Eighty years of

logo                                                      24 Jan 10, 14 July 10

optics of, post WWII     20 Mar 11

sextant frame stiffness                           28 Jan 10

sextant production, WWII                 14 July 10

shades adjusting tool                 6 Oct 13

tangent screw mechanism                      24 Jan 10,  24 June 11

telescope rise and fall mechanism          24 Jan 10, 24 June 11

polish, French                                                   24 Jan 10

Porro, Ignacio                              5 Oct 10

Poulin, Roger              29 June 14, 14 June15

pressure die casting                                           26 Oct 08,

working life of dies                                     14 July 10

prism, eyepiece, of AN5851                             9 Dec 08

Blish                             5 Apr 2012

Roof                            23 Apr 2012

removing from monocular                      18 Nov 09

protractor, three armed. See station pointer

quintant, vernier                                                30 May 09


Hezzanith                                              3 Jan 09

Hughes                                                 3 Jan 09

Heath                                                   24 May 09

Ilon Industries            1 Oct 14

C Plath Yachting sextant       14 June 15


paint, decay of                                       9 Dec 08

half life of                                             9 Dec 08

release catch

of La Filotecnica sextant     5 Oct 10

of US Maritime Commission sextant   15 Dec 10

of C Plath yachting sextant         14 June 15

Repsold      13 Nov 12

rising piece

bent, repair of    28 Apr 10,      20 Oct 16

collimating,    2 Sept 11

faulty construction of Tamaya    2 Sept 11

structure of, in Admiralty pattern sextant  24 June11

of Carl Plath’s earliest sextant        21 April 2017

in Ilon Industries sextant            1 Oct 14

in La Filotecnica sextant      5 Oct 10

in Troughton and Simms sextant    28 Apr 10

Salmoiraghi, Angelo       5 Oct 10

sapele                                                               24 Jan 10


glass                                                     22 Mar 09

ivory                                                     10 Nov 09

screwcutting conical threads                              6 July 09


broken, removal of                    24 May 09, 17 April 10, 20 Oct 16

grub, replacement of                          4 Mar 10

pin    29 Apr 10

tangent, of  Troughton and Simms sextant    28 Apr 10

of C Plath’s earliest sextant      21 April 2017

Service, US Maritime    15 Dec 10


Admiralty pattern     27 Mar 11

calibration of         13 Feb 11

cleaning of                                            23 Nov 08, 18 Feb 10

double. See double sextant

fake                                             14 July 10

left handed                                            2 Dec 08

small craft            14 June 15

survey. See survey sextant

Yachting             14 June 15


assembly of horizon                              18 Feb 10

assembly of index                                 18 Feb 10

carrousel of AN5851                            14 May 09

remounting index                                   18 Feb 10

repainting                                              18 Feb 10

shellac, sealing bubble chambers with    20 Dec 08

secondary sealing bubble chambers with   13 Oct 10

Simms, William      29 Apr 10

Skalensextant, Freiberger                                  22 Mar 09

bearing of                                             22 Mar 09

dimensions of                                        22 Mar 09

optical path of                                       22 Mar 09

prism, cleaning of                                4 Mar 10


lighting                                         22 Mar 09

focus screw, access to            4 Mar 10

focus of                                        4 Mar 10

SNO-M sextant (Navigation sextant with illumination, marine)

compared to C Plath                             26 Oct 08

origins of                                              26 Oct 08

telescope of                                          26 Oct 08

SNO-T sextant (Navigation sextant with illumination – tropicalised)

index arm bearing of                             22 Nov 08

instrumental accuracy of                        22 Nov 08, 13 Feb 11

micrometer of                                       22 Nov 08

mirror adjusting screws            17 April 10

use of                                               17 April 10

repair of                                          17 April 10

drawing of                                       17 april 10

origins of                                              22 Nov 08

position of index arm                             22 Nov 08

telescopes of                                        22 Nov 08


of tangent clamp                                    10 Nov 09

material of                                    10 June 10

of swing arm chassis     12 Mar 09

pre-load, of worm shaft     12 Mar 09,  15 Dec 10

Stanley, W F and Co, merger with Heath          26 Apr 09

station pointer                                                   26 Apr 09

survey sextant                                                   6 May 09, 26 Apr 09, 28 Apr 10

frame of                                                6 May 09

handle of                                              6 May 09

placement of legs                                  6 May 09

telescope mounting of                           6 May 09

use of                                                  26 Apr 09

swaging, of lens                                                24 Jan 10

swing arm

of Observator sextant       20 Oct 16

bearings, Heath                                5 May 09

chassis     12 Mar 09

Ilon Industries            1 Oct 14

keeper       14 June 14

switch, lamp, of Husun                          18 Feb 10

Tamaya, faulty rising piece,   2 Sept 11

tangent screw,

Heath                                                  28 Jan 10

Hezzanith endless                                 3 Jan 09

Hughes Admiralty pattern   24 June 11

of C Plath’s earliest sextant    21 April 2017

taper pin,

removal                                               18 Dec 08

replacement                                         18 Dec 08

sealing bubble unit with      5 Oct 10


collimation of     2 Sept 11

making                                                23 Nov 08

Galilean, optics of                                 30 May 09

of C Plath’s earliest sextant     21 April 2017

of C Plath WW II sextant                  14 July 10

of C Plath yachting sextant           14 June 15

of Hughes Admiralty pattern sextant          24 June 11

of La Filotecnica Salmoiraghi sextant     5 Oct 10

of SNO-M sextant                               26 Oct 08

of SNO-T sextant                                 22 Nov 08

of US Martitime Commision sextant   15 Dec 10

Willson bubble                          2 Dec 08

telescope mounting

of survey sextant                                   6 May 09

Husun                                                   24 Jan 10

telescope rise and fall mechanism, Plath 24 Jan 10

Admiralty pattern  24 June11

thread, interrupted of telescope mounting     5 Oct 10, 24 June 11

tool, shades adjusting, Plath           6 Oct 13

Troughton, Edward    28 Apr 10, 10 June 10

Troughton, John     28 Apr 10

US Maritime Commission  15 Dec 10

US Maritime Service   15 Dec 10

US Navy Bureau of Ships   Dec 10

vial, of spirit level                                              30 May 09

washer, Belleville                                              18 Feb 10

lead, for sealing filling hole in A10 bubble unit  13 Oct 10

making                                                 11 Aug 09

Wild, Heinrich                                                  22 Mar 09

Willson bubble telescope                                  2 Dec 08

Wollaston, William                                10 June 10


bent shaft of                                         6 July 09

burrs on                                               6 July 09

cutting new                                          6 July 09

errors     12 Mar 09

Hughes                                                3 Jan 09

Ilon Industries           1 Oct 14

periodic error of             6 July 09

progressive error of                              6 July 09


effects on plastic                                   18 Dec 08

refilling bubble chamber with ,              18 Dec 08, 13 Oct 10

resistance of Viton to, 13 Oct 10