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 .
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 , 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 . 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 , 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 . 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 . 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 email@example.com
 Personal communication with eBay seller
 See the earlier post titled 'What do the Number 3500 and 1542 Tell Us?, Part Two'
 See the 'Box Comparisons' photos at: https://tighar.org/wiki/Sextant_box_found_on_Nikumaroro
 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.