A Box Sextant

7 01 2010

All figures may enlarged by clicking on them. Use the back arrow to return to the text.

For a sextant enthusiast, to own a box sextant after handling  full sized instruments gives a lot of pleasure. These dainty and ingenious little instruments, measuring only 75 mm in diameter, can be slipped into a pocket, but be quickly brought out to make a reading with a precision of around an arc-minute. They are equipped with shades that allow sun and moon observations and some models come with a small telescope. They are especially handy for taking horizontal angles on land.

Unfortunately, there are many so-called reproductions on the market, and it may not be easy for the inexperienced to distinguish them from the genuine article. One should look for fine, usually straight  knurling on the adjusting knobs, crisp edges to the index arm and magnifier arm, sharp corners on the bracket that holds the latter, smooth, ground edges to the mirrors and sweet operation of the various adjustments. A bright sky should just be visible through the darkest shade (usually red) and should not be visible at all when used in combination with the second shade (usually blue). The two together should allow comfortable viewing of the full sun.

The scale is usually divided on silver, each degree being divided into halves, with a vernier reading to one minute. The arc radius is about 46 mm. Look for crisp regular engraving of the numerals (Figure 1) rather than the uneven, stamped numbering with rounded edges often seen in  reproductions. The numbering on the vernier usually omits the fives, and a scale with crowded numerals reading 5, 10, 15 etc is quite likely to be a fake. The scale is read from the centre of the index arm, the opposite of a nautical sextant, which is read towards the centre.

Scales 001

Figure 1: Scales of genuine antique.

A maker’s name  may be of little help. There must be thousands of so-called “Stanley” and “Kelvin-Hughes” instruments around, the latter usually dated 1918, nearly thirty years before  the real company came into being. Stanley was a highly respected firm of instrument makers and suppliers, founded in 1853 and trading well into the second half of the twentieth century. Older instruments are engraved “Stanley, London” in beautiful copperplate, though they were probably made (and later labelled) by Heath and Co, with whom Stanley eventually merged in 1926. There are box sextants bearing the name of Elliott Brothers and many other nineteenth century instrument makers and most of these are genuine, but it is important to look at the general workmanship as well as the name. Stanley is the name that has been most abused.

The second photo shows a genuine box sextant by Stanley, alonside its big brother from the same period, a vernier sextant of eight inches radius by Crichton of London, dated to about 1850. The lid unscrews to expose the controls, and is screwed on to the base to act as a handle in use.

 

The next photo shows the underside of the browned bronze base of the instrument. The nib is used to slide the cover aside. This opens the slot through which shades emerge when not in use, as will be seen in a later picture.

Figure 3: Base.

The general view below shows some of the main features. Rotating the control knob moves the index arm and the vernier over the scale while rotating the index mirror. Note the fine knurling and the crisp edges of the pin holes in the central screw. The magnifierarm, its bracket and the index arm also have crisp edges and the screw slots are narrow, the screw heads polished. Sliding the nib brings the peephole into position and a knurled screw is provided above the peephole to attach the telescope when it formed part of the kit (in some makes, the telescope screwed into the hole). Next to this screw is the mirror-adjusting tool, which screws into place. The levers for bringing the shades into and out of position are to the bottom left of the photo. When they are not in position, they project through the slot described in the preceding paragraph. At the top end of the scale can be seen the two square-headed screws which are used to adjust out side error.

The next photograph shows many of these features from a different viewpoint, that also shows the window opposite the peephole and the head of the screw used to adjust for index error.

For those of you who dare not take their instruments apart, in the next picture I have done it for you, by removing three screws from the periphery of the base plate. The shades are raised out of the way. In use, the head of a limit screw ensures their correct position. The index mirror, its bracket and keeper are mounted on a bearing and are rotated by the toothed sector or rack by means of the control pinion, the business end of the control knob. The horizon mirror sits on a base that can be rocked by means of two spring loaded screws to remove side error and the sub-base below it can be rotated by a further spring loaded screw to remove index error.

The next picture shows another view of the interior to show more details of the horizon mirror arrangement.

Thanks to the kindness of Bill Whiteley, I am now (October 2013) able to add a few sentences about the origins of the box sextant.

A memoir of a meeting appeared in The New Monthly Magazine, Vol 24  1828, of “…the late James Allan mathematical instrument maker in London, who died in the year 1821, compiled by the late Rev. Thomas Macfarlane, minister of Edinkillie, with an introductory letter by Sir Thomas Dick Lauder, Bart. Mr Allan was a native of the parish of Edinkillie, who procured to himself a considerable portion of fame by the discovery of several simple, but most accurate methods of graduating mathematical instruments. The pocket sextant, which gained him the prize and encouragement of the Society of Arts of London, was exhibited on the table of the institution at this meeting. It now belongs to Sir Thomas Dick Lauder.”

 A box sextant presented by the 4th Duke of Gordon to his son in 1813, signed by Allan, is now in the Royal Engineers Museum. This gives us a date before which the instruments were being made.
 
In Nov 1800 James Allan is a shopman (?foreman) lately in the employ of the famous Jessie Ramsden receiving a legacy from Mr Ramsden of twenty pounds. It seems that Allan remained at the Piccadilly workshop, (which had been inherited by Matthew Berge from  Jessie Ramsden,) and was in a position to operate independently. In Nov 1809 he presented to the Royal Society of Arts an improvement on the dividing machine created in 1775 by his former employer Jessie Ramsden. Meantime Berge had amongst other matters, been actively miniaturising the moderately short-lived bridge sextant an instrument which in all probability involved the attention of James Allan.
 There currently exists no firm date for Allan’s creation of his box sextant, However we might assume it to be around the time of his improvements to the dividing machine.
I hope to be able to add a little more about the origins of the box sextant when Bill has had a chance to trawl through the Proceedings of the Royal Society of Arts in the British Library.
12 November 2016: Richard Paselk , Professor emeritus at Humbolt University has kindly just send me this link describing some more of the history of the box sextant: http://www2.humboldt.edu/scimus/AvH_HSU_Centenial%20Exhibit/Box_Sextant/BoxSextant.htm 

Finally, this picture, showing the instrument in use, gives another impression of its size.

If you enjoyed reading this post or found it helpful, do let me know and if you have a “doubtful instrument” I will be happy to view a photo and advise.

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14 responses

15 02 2010
Andy

You have a very fascinating website. I have a 1939 H. Hughes & Son vernier sextant in pristine condition. What really got me though was your box sextant. I have one very similar to yours. The only difference being the absence of the telescope attachment screw. Mine is labelled Stanley London, made in England, and has Arabic script and numerals engraved on the base. This is not surprising as I picked it up in a souke (antique market) in Cairo. My belief is it was used by the surveyors who mapped out the Egyptian railway network post WWI. Mine is complete with leather case and a dark screw-on filter for the in-built telescope. I don’t find it of much use at sea but as the arc goes to 145 degrees I can use it onshore with an artificial horizon.

Regards
Andy

16 02 2010
engineernz

Thank you, Andy.

I will shortly be posting an account of a1939 Husun three circle sextant that came to me a a box of mud-covered bits and which is now again in a pristine condition too.

KInd regards

Bill

24 02 2010
Andy

The serial number of my H. Hughes sextant is 22784. The certificate in the box lid is dated 21st July 1939 and declares the sextant to be Class A with no corrections required across the arc. The vernier resolves to 10″ of arc but is a lot harder to read than a micrometer drum.

Following your box sextant guidelines I stripped mine down for a clean and lub. What I thought to be a cover meant to slide down over the telescope is in fact the peephole sight used when you unscrew the telescope from the sextant. The telescope collapses fully within the sextant body.

I’d be happy to send you pictures of both sextants but I don’t see an e-mail address in this blog/website.

23 09 2011
Daren Whistler

Bill,

Thanks for a very informative webpage, I have just purchased a Newman & Guardia box sextant no. 4790 dated 1918 on an impulse buy.

As an ex British Army engineering surveyor I am familiar with survey instruments and the like but am very keen to source a instruction book or original pamphlet on the use of the sextant, do you know of such a thing exists ?

23 09 2011
engineernz

Thank you Daren. I am sending you some pages from “Surveying” by W Norman Thomas, London, 1926., that give information about the principles, use and adjustment of the box sextant. Anyone else who would like a copy of these pages for personal study please Contact me.

Bill

31 01 2012
Martin Hoskins

Bill

Really facinating webpage, I have a 1916 Box Sextant by Frankham, it looks exactly like yours. I have been using a book by Jack Case as a guide, and am producing a small notebook of his rules for taking noon readings. I was interested to see the previous message about surveying as mine unit was used by the RAF, possibly for mapping airfields ?? so I would really appreciate a glimpse at it as well please.
I was wondering about your thoughts on the safety and effectivness of the filters for a unit of this age, it has the red and green, and in addition to the peep hole it has a minute dark filter, presumably pre polorizing?

31 01 2012
engineernz

The safety of shades comes up periodically, in the context of worries about ultra-violet rays penetrating to and damaging the retina. In the 1960’s there were people who gazed at the sun under the influence of drugs and whose retinas on the whole came to remarkably little harm, and of course, there was their famous predecessor, Isaac Newton. Ultra-violet rays are quite well absorbed by ordinary glass and I would take the pragmatic view that if one can view the sun comfortably, the filters are satisfactory. Polaroid had not been invented in 1916 and, though older books write about a Nicol prism being used to reduce horizon glare, I have yet to see one. From about 1938 onwards, sextants were occasionally fitted with crossed Polaroids as shades, notably the US Navy Mark II, and I have an instrument from 1967 that has them, but I find that the view of the sun is just on the edge of being too bright for comfort.

Bill

18 05 2013
Arthur

Thanks Bill, I just bought this intriguing piece of craftmanship on the market today. The device has had a usefull life, judging from the wear of the paint. However it operates well. Mine is engraved “Stanley gt. Turnstile”, from wiki i read this relates to the town where Stanley was based. No serial number nor other engravings. I wonder what the date of manufacturing is. The vernier scale reads 0/10/20/30. It has a small external telescope, with a screw on cover, to protect the small lens (cover for big lens missing?). The leather case is worn, but can be repaired. All in all a nice gadget. Could you send me a copy of “Surveying”, 1925? Thanks in advance.

18 05 2013
xotdog

Thanks Bill, I just bought this intriguing piece of craftmanship on the market today. The device has had a usefull life, judging from the wear of the paint. However it operates well. Mine is engraved “Stanley gt. Turnstile”, from wiki i read this relates to the town where Stanley was based. No serial number nor other engravings. I wonder what the date of manufacturing is. The vernier scale reads 0/10/20/30. It has a small external telescope, with a screw on cover, to protect the small lens (cover for big lens missing?). The leather case is worn, but can be repaired. All in all a nice gadget. Could you send me a copy of “Surveying”, 1925? Thanks in advance.

20 05 2013
engineernz

I am away from home at the moment. Would you please send me a reminder about the pages from “surveying” in about a weeks time?

Bill

25 11 2013
Bruce

Are their drawings available for any of the older box sextants? I would love to try to reproduce one.

13 04 2014
Mike Gmoser

Great article. Just purchased Hobbs and will hope to communicate with you on its genuineness and function.

27 10 2014
Richard Paselk

Hi Bill, to add to your history, the box sextant was first described by William Jones in 1797 and is often attributed to him as inventor. I have provided a pdf of his description linked to a description of a box sextant in my collection. You can find the description at: http://www2.humboldt.edu/scimus/AvH_HSU_Centenial%20Exhibit/Box_Sextant/BoxSextant.htm
The link to Jones is in the first paragraph below the photo of the sextant.

Thanks for your continuing work on sextants! I treasure both your sextant book and your chronometer book as terrific contributions to the literature on both instruments.

Cheers,

Rich Paselk

16 04 2015
Tony Cousins

What great information i have an almost identical fully working box sextant. not sure when i acquired it. Once upon a time i worked with the Ordnance Survey revising the inch to one mile maps of the UK..
My one however has the maker as “T.A.R.S. & W”
B 986
^
With a an upward pointing arrow underneath not just ^ i also have a good case with slightlly damaged strap.

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