Friday, December 15, 2017

Brandis Sextant Taxonomy, Part Six: U.S. Navy Sextant Specifications

Brandis Catalog No. 20, which I’ve referred to in several earlier posts, tells us about a few key features of four different Brandis sextant types.  A great deal more information about three of these sextant types can be found in the sextant specifications that were published from time to time by the U. S. Navy.  The Navy began publishing specifications for sextants in the 1890s with the aim of improving the quality of the sextants produced for it by instrument manufacturers.  As explained in the Department of Nautical Instruments section of the U. S. Naval Observatory’s Annual Report for fiscal year 1895 [1]:

The province of this department is to receive, inspect, and issue to the vessels of the Navy all instruments (chronometers and watches excepted) furnished for navigating and surveying purposes.
In order to put this important service upon a proper basis and to assure its systematic working whereby the best instruments can be obtained, detailed specifications have been prepared with great care for sextants, high-grade and surveying; octants; binocular glasses, day and night; quartermaster’s spyglasses, high, medium, and low power; officer-of-the-deck spyglasses; barometers, mercurial and aneroid; clocks, deck and boat; three-arm protractors, and theodolites.

A complete outfit of the apparatus necessary to the thorough inspection of instruments has been provided for and will soon be installed for use. Contractors have experienced some difficulties in fulfilling the requirements of the specifications, but better progress in that direction is now being made, and by rigidly enforcing the specifications our ships are being supplied with instruments of the above classes uniform in pattern and excellent in quality.

I have copies of the U.S. Navy’s surveying sextant specifications published in 1897 and 1901, its high grade sextant specifications published in 1897, and its specifications for octants published in 1900 [2].  Each of these documents is four pages long and consists of a series of numbered sections stipulating the features of a particular sextant component or accessory.  The sextant features described in Brandis Catalog No. 20 match up well with those put forth in the specifications, even though Brandis Catalog No. 20 was published about 15 years after these specifications appeared [3].  For example, the catalog listing for the “U.S. Navy Surveying Sextant” states that it has a 6-inch radius and reads to 30 seconds of arc, while the 1901 surveying sextant specifications requires a frame radius not less than 5.75 inches nor more than 6.0 inches and a vernier scale providing a reading precision of 30 seconds of arc; the catalog listing for the ‘U.S. Navy High Grade Sextant’ states that it has a 7-inch radius and is readable to 10 seconds of arc, while the 1897 high grade sextant specifications require a frame radius between 7 and 7.5 inches and a vernier scale providing a 10 second reading precision; the catalog listing for the ‘U.S. Navy Octant’ states that it has a 7-inch radius and is readable to 30 seconds of arc, while the 1900 octant specifications require a frame radius between 7 and 7.5 inches and a vernier scale providing a 30-second reading precision.

Something I find curious about the Navy surveying sextant specifications is that they require surveying sextant frames to have four radial arms “stiffened by one transverse brace, which shall be an arc of a circle concentric with the limb”.  The ‘U.S. Navy Surveying Sextant’ illustrated in Brandis Catalogue No. 20 (see illustration below) has the required curved transverse stiffener brace, but it also has a second, straight, transverse stiffener brace, and I’ve seen many Brandis surveying sextants made for the Navy that have this frame pattern.  I’ve also seen surveying sextants made for the U.S. Navy by two other U.S. manufacturers, Keuffel & Esser, and Buff & Buff, that have two transverse braces, although these surveying sextants have two curved transverse stiffener braces [4].  It seems that these three sextant manufacturers believed that two transverse braces were needed to give their Navy surveying sextant frames sufficient stiffness, so then why is it that the Navy surveying sextant specifications required only one transverse brace?

There are only a few differences between the surveying sextant specifications published in 1901 and those published in 1897.  One such difference is in the specification for the tangent screw used to make fine positional adjustments to the sextant’s index arm.  The 1897 specifications call for a single-headed, 4.1-inch long, tangent screw, while the 1901 specifications call for a two-headed, 2.75-inch long, tangent screw.  This arcane difference is of interest to me because I’ve collected photos of dozens of Brandis sextants that I’ve found on eBay and other web sites, and many of these photos provide a good view of the sextant’s tangent screw.  When I went through my photo collection I was able to clearly identify twenty-two of them to be surveying sextants [5].  Of these twenty-two surveying sextants, only the oldest of them, Brandis serial number 1899 [6], has a long, single-headed, tangent screw.  The rest of them, spanning a range of Brandis serial numbers from 2539 to 5675, have a short, two-headed tangent screw (see table and photos below).

Brandis Surveying Sextant Serial Numbers and Tangent Screw Types

Brandis #1899

Brandis #2539
Brandis #5675

If it is assumed that Brandis manufactured these sextants to U.S. Navy specifications [7], then Brandis #1899 must have been made no later than 1901, the year that surveying sextant specifications calling for the shorter tangent screw was published [8].  The ‘no later than’ date for the manufacture of Brandis #1899 provides an additional reference point for the Brandis serial number chronology that was presented in ‘What do the Numbers 3500 and 1542 Tell Us? Part Two’.  Some time in the not-too-distant future I will post a revised version of the Brandis serial number chronology that will include the reference point provided by Brandis #1899 as well some others I’ve arrived at since that chronology appeared.

If there is a master list of all U.S. Navy sextant specifications ever published, I have not seen it, but I do know that the four specifications I have copies of aren’t the only ones ever published.  According to the National Directory of Commodity Specifications [9], the Navy published surveying sextant specifications in 1912 and high grade sextant specifications in 1914.  An article in the July 24, 1918 issue of the trade journal  Jeweler’s Circular Weekly, which is reproduced in the post titled ‘What do the Numbers 3500 and 1542 Tell Us? Part Three’ reports the recent publication of Navy surveying sextant specifications and states that these new specifications supersede those published in 1912.  I know that octant specifications were published in 1895, because my copy of the 1900 octant specifications ends with the statement “Reprint of May 20, 1895. No change”.  I have not found any indication of the existence of specifications for either of the other two Brandis sextant types discussed in earlier posts, the astronomical sextant listed in Brandis Catalog No. 20, or the Brandis sextant with the 5-inch radius frame whose name I am uncertain of.

I would like to have copies of all the U.S. Navy sextant specifications ever published.  If I knew what changes the 1918 surveying sextant specifications called for relative to 1912 specifications, I might be able to find where in my collection of Brandis sextant photos those changes first appear and so add another dating reference point to the Brandis serial number chronology.  If the Navy published specifications for the 5-inch sextant type whose name I am uncertain of, I’d have a definitive name for this sextant type.  There are some specific changes I’d expect to see in versions of the sextant specifications that published after the ones I have copies of.  For instance, each of the four sextant specifications I have copies of require that sextants be supplied to the Navy in sextant boxes having a brass plate sunk into the top of their lids.  The purpose of this plate is made clear in the octant specifications, which states that the manufacturer was to mark the plate with the sextant’s Naval Observatory number, the Naval Observatory hallmark (the letter ’N’ inscribed with the letter ‘O’), and the words ‘U.S. Navy’ upon acceptance of the sextant by the Navy.  I’ve seen these plates in the lids of Brandis sextant boxes made before World War One (see photo below), but not in the lids of Brandis sextant boxes made during World War One and so I suspect that the specifications in effect during the war no longer required them; it would be nice to to read those specifications to see if this is in fact true.

Box Plaque for Brandis 2763/USNO 348, an Octant

I’ve looked at sextants made by two of Brandis’ U.S. competitors to see how well they match up with the Navy specifications, but I’m not sure I can quickly summarize what I found so I’ll save that discussion for another post.  I’ll end this post by repeating something I may have mentioned in an earlier post, and that is that I’ve seen a few Brandis sextants that don’t match any of the sextant types listed in Brandis Catalog No. 20.  Some of these sextants have features that don’t jibe with the specifications that I have copies of.  This too is something that requires more than a brief discussion, and so I will save it for a future  post.
UPDATE (12/17/2017):
Having written only two days ago that Brandis #1899 is the only surveying sextant I’ve seen that has a long, single-headed tangent screw, this morning I came upon a second Brandis surveying sextant, Brandis #1839, with this type of tangent screw. The Brandis serial number and ‘U.S. Navy’ is stamped into the arc, as per a few other old Brandis sextants, and the front of the box is marked ‘Sur Sex 1839’.  A scrap of a Naval Observatory certificate remains, enough to see first two digits of the Brandis serial number and the letters ‘Su’ on the line for sextant type.  See photos and updated table below.

Comments, corrections, additional relevant facts, differing viewpoints, etc., are always welcome.  Send to
[1] Report of the Superintendent of the U.S. Naval Observatory for the Year Ending June 30, 1895.  Washington.  U.S. Government Printing Office, 1896. Page 116.
[2] These four sextant specifications were copied onto microfiche by the Congressional Information Service and are available at libraries around the United States. U.S. Executive Branch Documents, 1789-1909; numbers N-507a -241,-269,-270, and -271.
[3] See the post titled ‘A Brief Note on the Date of Publication of Brandis Catalogue No. 20’ published on February 16, 2017.
[4] The frame pattern of Keuffel & Esser and Buff & Buff surveying sextants, however, differs from Brandis surveying sextant in that both transverse braces are curved.  The K&E and B&B sextants I refer to here have Naval Observatory inspection certificates identifying them as surveying sextants.
[5] I determined each sextant to be surveying sextant if it’s frame had one straight and one curved stiffening brace and at least on of the following was true: there was a Naval Observatory inspection certificate for the sextant identifying it to be a surveying sextant, or the sextant’s arc scale was divided in 20 minute intervals.  Both cases were often true. 
[6] Brandis #1899 is not marked with  U.S. Naval Observatory serial number but we can be sure it was once in U. S. Navy service because ‘U.S. Navy’ is stamped into its limb, as can be seen in the photo of this sextant in this post. 
[7] Note that most of these sextants in Table 1 have a U.S. Naval Observatory serial number, indicating they were inspected to Navy specifications at the Naval Observatory.  Note also that Brandis Cat No. 20, which was aimed at the civilian market, calls its surveying sextant a ‘U.S. Navy Surveying Sextant’, which suggests to me that even the surveying sextant that Brandis sold to civilians were made to Navy specifications.
[8]  Most of the sextants in Table 1 were made during World War One, thus if Brandis manufactured them to U.S. Navy specifications, then the Navy surveying sextant specifications in effect during World War One must have required the short, two-headed tangent screw.
[9] National Directory of Commodity Specifications. National Bureau of Standards U.S. Government Printing Office, 1925. Page 289. This can be found online at Google Books.