We Have a Winner!

In my post on Brandis Astronomical sextants, I offered a lifetime GoG blog subscription to the first person to explain the purpose of the small spirit level attached to the index arm of sextants of this type.  It took only four days for a reader, whom I will identify as ‘C.V.’ [1], to come up with the answer to this puzzle.

C.V. referred me to two books, 'Wrinkles in Practical Navigation', published in 1918, and 'Hints to Travelers', published in 1871 [2,3].  Apparently, the idea of putting a spirit level on the index arm of a sextant originated with Karl Friederich Knorre (1801-1883), Professor of Practical Astronomy at the School of Navigation in Nikolaev, a major Black Sea port city in what is now Ukraine.  The purpose of the spirit level was to allow someone measuring the altitude of a celestial body with the aid of an artificial horizon to ensure that the measurement was being made correctly.  An artificial horizon is a container holding a pool of reflective liquid, usually mercury, that allows a sextant user to measure the altitude of a celestial body when a proper horizon, such as can be seen on a clear day at sea, is not available [4].  The user first locates the image of the celestial body in the reflective surface of the artificial horizon and then ‘brings down’ into alignment with it the image of celestial body reflected from sextant’s index mirror; dividing the resulting angle by two gives the altitude of the celestial body.  Apparently, it was fairly easy to mistakenly ‘bring down’ the wrong celestial body when a similar-looking celestial body was close in the sky to the correct one.  The index arm spirit level prevents the user from making this error.  Its angle relative to the index mirror is such that the level’s bubble will ‘play’ when two images of the same celestial body are in alignment.

Many thanks to C.V. for solving the puzzle of the index arm spirit level.  Congratulations on your lifetime subscription to the GoG blog, C.V.!  To all my other readers, there's still hope: A second lifetime subscription is still available to the first person to find a surviving example of a Brandis Astronomical sextant.

+~+~+~+
[1] Although C.V. has given me permission to use his full name, in the name of protecting the innocent only his initials will be used
[2] 'Wrinkles in Navigation' can be downloaded at: https://archive.org/stream/wrinklesinpracti00leckrich#page/n7/mode/2up
[3] 'Hints to Travelers' can be downloaded at:
http://galton.org/essays/1870-1879/galton-1871-jrgs-hints-travellers.pdf
[3] More on artificial horizons can be found at: http://www.longcamp.com/horizon.html

Brandis Sextant Taxonomy, Part Four: Astronomical Sextants

A fourth type of sextant that Brandis was making around the time of the first World War was the Astronomical Sextant.  As in the last three posts, Brandis Catalog No. 20, published sometime between 1915 and 1917, provides a nice illustration of this sextant type.

The catalog description tells us that these sextants have a 6-inch radius and that they provide a 10-second measurement precision.  What stands out to me is the frame pattern, which is quite different and more aesthetically pleasing to my eye than the frame pattern shared by the three sextant types discussed in my earlier posts in this series.  Astronomical sextants also appear in the 1895 Brandis catalog, and here we are told that they owe their frame pattern to a Professor Harkness.  This must be Professor William Harkness, who among other things was Astronomical Director at the U.S. Naval Observatory and inventor of numerous astronomical instruments [1].  As an aside, the 1895 Brandis catalog refers to the plainer Brandis frame pattern of the other Brandis sextant types we've looked at as the ‘Gambey Pattern', presumably after  Henri Prudence Gambey, a French instrument maker of the early 19th century [2].  The Smithsonian has in its collection a 19th century Gambey sextant made for the U.S. Coast and Geodetic Service that looks to be a very close match for a Brandis high grade sextant in terms of its frame pattern and other features [3].

I’ve seen forty-five or so Brandis sextants and not one of them is an astronomical sextant.  However, the Smithsonian has two sextants made by Stackpole and Brother (Stackpole #1765 and #2258) that look very much like a Brandis astronomical sextant.  An excellent high-resolution photograph of #1765 can be found on the Smithsonian’s website [3].  It may be significant that F.E. Brandis worked for Stackpole and Brother for several years before founding his own instrument company [4]. 

An unusual feature we can see in both Brandis catalog illustrations and in the photo of Stackpole #1765 (the photo of #2258 is too poorly resolved to tell) is that these sextants have a bubble level attached to their index arms.  A bubble level attached to a sextant’s index arm wouldn’t allow a user to hold the sextant level in the absence of a visible horizon as in a Byrd sextant, so what purpose these levels serve eludes me.  The description of Stackpole #1765  at the Smithsonian’s website has this to say about the level: “The sextant also has a small bubble level on the index arm. William Harkness, the American astronomer who introduced this feature, said that it "proved a very great convenience and saved much time and trouble.”  How the index arm level saved time and trouble we are not told, unfortunately.  The only other sextant I’ve ever seen with a bubble level on its index arm is a Cary sextant that can be seen on the Tesseract website [5].  The Cary sextant’s bubble level is perpendicular to the long axis of the index arm, while in the case of the Brandis and Stackpole sextants the bubble levels are not perpendicular to that axis.

The first person to explain to me what what function these index arm bubble levels served gets a free lifetime subscription to the Ghost of Gardner blog.  The same goes for the first person to find a photo of a surviving Brandis astronomical sextant.

Comments, corrections, additional relevant facts, differing viewpoints, etc., are always welcome (no one will be banned, blocked, or castigated for offering differing opinions).  Send to gardnersghost@gmail.com
+~+~+~
[1] Harkness' obituary appears in the April 17, 1903 issue of Science, the journal of the American Association for the Advancement of Science. In 1893, Harkness was president of the AAAS. See: https://books.google.com/books?id=HY8CAAAAYAAJ&pg=PA601&dq=william+harkness&hl=en#v=onepage&q=william%20harkness&f=false
[2] http://americanhistory.si.edu/collections/search/object/nmah_1183824
[3] http://amhistory.si.edu/navigation/object.cfm?recordnumber=1183824
[4] http://amhistory.si.edu/navigation/maker.cfm?makerid=35
[5] http://www.etesseract.com/Navigation/Navigation.html

Brandis Sextant Taxonomy, Part Three: Octants

A third type of sextant that appears in Brandis Catalog No. 20 is the ‘U. S. Navy Octant’, shown below.  We are told that it has a radius of 7 inches and provides a measurement precision of 30 seconds, and we can see that its frame is comprised of three radial arms crossed by two curved stiffener braces.

Out of the forty or so Brandis sextants that I’ve seen well enough to identify as to type, only one, Brandis #2763/USNO #348, shown below, appears to be an octant (note: see update below). A dated sales label in the box for Brandis #2763/USNO #348 suggests that it was made in 1911 [1] .

I was surprised to learn that Brandis was still making octants into the early decades of the twentieth century [2].  All of the octants I’d seen in museum collections were made in the 19th century or earlier, and while researching the Brandis sextants I’d come across a recommendation in the U.S. Naval Observatory’s Annual Report for fiscal year 1890 that “no more octants to be purchased or repaired, and none of the latter to be issued after the present supply be exhausted”.  Yet it seems that the U.S. Navy ignored the advice of the Naval Observatory, perhaps motivated by their price compared to other types of sextants.  According to Brandis Catalogue No. 20, octants could be purchased for $95, while high grade and surveying sextants went for $130 and $120, respectively.

I note that Brandis’ competitor Keuffel & Esser also lists an octant “as made for us for the U.S. Navy” in its 1913 catalog [3] but it no longer lists an octant in its 1921 catalog [4], so Keuffel & Esser stopped making octants sometime around World War One, presumably because there was no longer customer demand for them.  Of eight or so sextants I’ve seen that were made by Brandis’ competitors, one of them, made by Keuffel & Esser some time before the first World War, is an octant.

After the first World War, octants made a comeback of sorts for use in air navigation. But these were an entirely different kind of instrument from nautical octants like Brandis #2763/USNO#348.
+++
UPDATE (5/30/2018): A second Brandis Octant has come to light on eBay. Its Brandis serial number is 2679, but no indication in the eBay listing of a Naval Observatory number.  A Brandis label in its box indicates a delivery date of 1/19/11.

Comments, corrections, additional relevant facts, differing viewpoints, etc., are always welcome (no one will be banned, blocked, or castigated for offering differing opinions).  Send to gardnersghost@gmail.com
---
[1] See ‘A Brandis Sextant Chronology, Part Two’
[2] Brandis #2763/USNO#348 has a the 1911 manufacture date, and Brandis Catalog No. 20 was published sometime between 1915 and 1917
[3] “Catalogue of the Keuffel & Esser Co., Manufacturers and Importers of Drawing Materials and Surveying Instruments, Issue 34” Keuffel & Esser Co., 1913.
[4] “Catalogue and Price List of the Keuffel & Esser Co., Manufacturers and Importers Drawing Materials, Surveying Instruments, Measuring Tapes”, Keuffel & Esser Co., 1921

Brandis Sextant Taxonomy, Part Two: High Grade Sextants

A second sextant type that appears in Brandis Catalog No.20 is the ‘U.S. Navy High Grade Sextant’.  The catalog listing tells us that it provides a 10 second measurement precision and has a frame with a 7-inch radius.  Its frame pattern consists of four radial arms crossed by two curved stiffener braces, making it readily distinguishable from Brandis surveying sextants.

A few weeks ago a very nice example of a Brandis high grade sextant came up for auction on eBay. Two photos of that sextant taken from the eBay listing are reproduced below.  Its frame pattern and radius matches the high grade sextant listed in Brandis Catalog No. 20, and its arc scale is marked in 10 minute intervals, which is a sensible way to graduate the arc scale of vernier sextant meant to be read to a precision of 10 seconds. Unfortunately, none of the eBay photos provided a view of the vernier scale.  Its eBay seller reports its Brandis serial number to be 2864 and says that it does not have a U.S. Naval Observatory number [1].

I’ve had little luck finding other Brandis sextants that match the high grade sextant listed in Brandis Catalog No. 20.  A Brandis sextant with serial number 3193 in the collection of the Smithsonian museum has been a long-standing puzzle to me in this regard.  According to the description of this sextant on a Smithsonian web site [2], Brandis #3193 is a standard U.S Navy high grade sextant, or at least started out as one:

“This is a standard "U.S. Navy High Grade Sextant" that was made in the period 1914-1916 and modified in the early 1920s. It has a Willson bubble telescope, a Fischer rapid release lever, a drum micrometer, an electrical light over the divided arc, and a battery in the handle. The National Bureau of Standards transferred it to the Smithsonian in 1957. ”

According to the Smithsonian, the frame of Brandis #3193 has a 7-inch radius and the photo that accompanies this description shows that the frame has four radial arms and two curved stiffener braces, like the high grade sextant in Brandis Catalog #20.  But while Brandis #3193’s frame is of the same size and has the same pattern as a Brandis high grade sextant, a detailed photo reveals that its limb has a rack, i.e., a series of teeth, at its periphery, and that its arc scale is divided only in one-degree intervals (a portion of this photo is reproduced below).  A rack is a component of the fine positional adjustment mechanism for the index arm of a micrometer sextant, but not of a Brandis vernier sextant, whose index arm is adjusted using a clamp-and-tangent screw mechanism. In the above photo of Brandis #2864 in its box, the clamp can be seen on the sextant's arc, connected to the index arm by the tangent screw.  Once the clamp is fixed to the arc (the thumbscrew for doing so is visible in the photo), turning the tangent screw causes the index arm to rotate clockwise or counterclockwise around its pivot point depending on which way the tangent screw is turned.  One-degree arc scale markings are suitable for Brandis #3193 because the micrometer drum scale is read to determine where a measured angle falls between those one-degree scale markings to the desired precision.  But the arc scale of a vernier sextant must be marked in fractions of a degree to be read to a precision useful for celestial navigation; the photo of Brandis #2864 shows us that the arc scales of Brandis high grade sextants are marked in 10 arc-minute intervals.  So Brandis #3193’s arc scale, like its rack, is not a feature of a Brandis high grade vernier sextant.

Are the rack and arc scale modifications to a Brandis high grade vernier sextant frame?  When I compare the limb of Brandis #3193 to that of Brandis #2864, it doesn’t seem to me that the latter can be a modified version of the former.  Could it be that the rack and one degree arc scale are original to the frame, i.e., that the frame was made to be an aeronautical micrometer sextant frame?  If Brandis serial number 3193 appears somewhere on the frame, the answer is ‘No’, because Brandis serial number 3193 corresponds to a manufacture date no later than 1917 according to the Brandis serial number chronology [3].  From what I’ve read, Brandis didn’t start making micrometer sextants until after the first World War, when it began manufacturing air navigation sextants.  Curiously, I can’t find a Brandis serial number on any part of the sextant that is visible in my detailed photo; normally the serial number appears on the front of either the limb or the index arm.  However, front side of the sextant’s index arm is marked with the ‘Brandis & Sons Mfg. Co.’ firm name that Brandis operated  under for several years ending in 1917 [4], and so the index arm, at least, was made no later than 1917.  Could it be that this sextant consists of a pre-war vernier sextant index arm attached to newer, micrometer-friendly sextant frame?  I don’t find this idea particularly appealing: if you’ve gone to the trouble of making a brand-new micrometer sextant frame, why put the index arm of an old vernier sextant on it?  I hope to eventually solve the puzzle of how and when this sextant was made but for now I consider the jury to be out on what kind of sextant this is and what serial number, if any, it was assigned by Brandis.

The trail grows even colder after Brandis #3193.  None of the many other Brandis sextants I’ve seen match the features of U.S. Navy high grade sextant in Brandis Catalog No. 20.  A few of them don’t quite fit into any of the types of sextants I can classify, and one or two of these sextants could potentially be later versions of a Brandis high grade sextant, but I will leave discussion of these sextants for a later post.  There is a hint that a sextant box owned by Tighar may have once held a Brandis high-grade sextant.  At the Tighar web site there are two photographs that provide side-by-side comparisons of three sextant boxes [5].  Two of these boxes still hold their original sextants, both of which appear to be surveying sextants.  The third sextant box also holds a surveying sextant but according to Tighar this sextant is not the box’s original occupant.  Markings on this third sextant box indicate that the original sextant it held was Brandis #3527/USNO#1599.  This third sextant box is larger than the other two, and since high grade sextants are larger than surveying sextants I wonder if Brandis #3527/USNO #1599 was a high grade sextant [6]. This is a question that can potentially be answered because there is a Naval Observatory inspection certificate attached inside the lid of this sextant. That certificate, if it is for Brandis #3527/USNO #1599, quite possibly indicates its type.

Comments, corrections, additional relevant facts, differing viewpoints, etc., are always welcome (no one will be banned, blocked, or castigated for offering differing opinions).  Send to gardnersghost@gmail.com
+~+~+~
[1] Personal communication with eBay seller
[2] http://amhistory.si.edu/navigation/object.cfm?recordnumber=123457
[3] See the earlier post titled 'What do the Number 3500 and 1542 Tell Us?,  Part Two'
[4] Ibid.
[5] See the 'Box Comparisons' photos at:  https://tighar.org/wiki/Sextant_box_found_on_Nikumaroro
[6] Tighar indicates that a sticker inside the box suggests that it once held an aeronautical bubble sextant.  I don’t think the box was enlarged to hold a bubble sextant, which had additional components.  Although a few small newer (lighter colored) pieces of wood are seen in the interior of the box, the external walls of the box are of a uniform, darker color.