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A mysterious elliptical compass

There are some drawing instruments that seem almost designed to stand out from the crowd, be it aesthetically or as the result of a radical departure from established archetypes. One such example that recently came into my possession scores highly on both counts. It takes the form of a deceptively large elliptical compass with a rather unique, if unpromising looking, mechanism and marked with a mysterious monogram. Previously I had seen the same design on a couple of occasions – it’s not something that is easily forgotten – but each time with different markings and retailers.

The first of these was retailed by J H Steward, likely before 1913 when the company was incorporated as J H Steward Ltd. It bears the same mysterious mark (“TG”?) and “déposé” stamp as mine, but differs by the addition of a scale of “English Inches” along the outer leg and the label “Centimetres” squeezed in between the original scale and the aforementioned monogram. Presumably these modifications were made specifically for the British market, possibly by the original maker if the consistency in division and numbering style is any indication.

JH Steward Taguel elliptical compass details

The other variant of which I am aware belonged to the now sadly dispersed collection of the late Robert Tolson. This lacks the stylised monogram, but is stamped instead with what looks like “TAGUEL” (could this be the “T” in the monogram?) as well as having a simpler form of “trident” leg than the other two. The set itself was retailed by Radiguet Opticien, 15 Boult des Filles du Calvaire, Paris, as described in the listing of this 2018 Bonhams auction for what is almost certainly the Tolson set (dated to around 1870, it sold for a tidy £1375). It is, however, unlikely that Radiguet was the actual manufacturer.

Returning to my example, it therefore came as a surprise to find that the somewhat distressed case was clearly labeled inside with yet another maker’s name: Baraban. It seems that Baraban was at the address 175 rue Saint Honoré from 1866 until 1874, after which he was succeeded by L. Thomas who continued to use the Baraban name in addition to his own. Comparing the detail of this instrument with others made by Baraban reveals some similarities, particularly in the design of the compass head and grip (see also this unusual Baraban-Thomas set at Worthpoint), as well as sharing the characteristic square leg section and division style of the radical Baraban-Thomas proportional dividers.

Baraban Taguel elliptical compass in its case

The similarities are sufficient to make me wonder if all three examples of this compass were manufactured by Baraban. However, this still does not explain the meaning of the monogram/Taguel marks, nor have I discovered the patent referred to. A device working on a similar principle, but with a more complex mechanism for setting the axis sizes was the subject of Austrian patent 25874 of 10 October 1906, applicant Alfred Triebling; an earlier example of the template type compass can be found in French patent 1BB11210, Lourdel/Lemonnier “compas à ellipse” of 1851; a later one by Johann Guenter & Johannes Saupe, French patent 646998, 12 Jan 1928.

Finally, after much searching, I managed to find a brief but enthusiastic mention of Taguel’s elliptical compass in La Nature: Revue des Sciences of 1 June 1878, having been one of the exhibits shown at the inauguration of the Exposition Universelle held in Paris that year (my translation follows):

Mr. Taguel is entitled to the recognition of mathematicians, engineers and architects for his compass which allows ellipses to be drawn as easily as circles, instead of resorting to the insipid operation of tracing the curve by points or with a thread. Delicate models of the machines are made with the finish of a timepiece.

How long it had been in production for by this date is unclear, nor have I since had any luck finding the related patent, as INPI draws a blank on Taguel.

Moving on to the operation of the compass, the concept is a simple one, although arguably not a true ellipsograph but perhaps more properly an oval-drawing compass. Mounted on the fixed trident leg is a three-dimensional template, the horizontal cross section of which changes along its vertical axis, from circular at the bottom to a narrow ellipsoid at the top. Importantly, the major axis of any given cross section is the same as the diameter of the circle at the bottom, so when looking at the template with the compass laid flat, it will be noticed that its sides appear parallel with the compass leg.

Baraban Taguel elliptical compass details

This arrangement allows the length of the major axis to be altered by sliding a wheeled collar up or down the movable drawing leg of the compass, which is correspondingly graduated along its length in centimetres. A spring mechanism concealed inside the compass head keeps the wheel in contact with the template at all times. Having selected the axis length, the template is then moved up or down the fixed leg until the desired sectional profile coincides with the position of the wheel.

I have found that the best way to achieve this in practice is to correctly locate the compass on the drawing surface with both major and minor axis lines marked, rotate the pencil point around to the minor axis so the wheel lies on the narrowest part of the template and then slide the template up the fixed leg until the pencil point reaches the end of the axis on the drawing. This way, both axes can be set relatively quickly, certainly compared to other types of true ellipsograph.

Drawing the ellipse is then a simple one-handed operation, very much like using a regular compass, albeit taking care to keep the fixed leg vertical. The fixed leg itself cannot rotate due to its three points; instead the compass head pivots on top of the leg, marked by a circular steel washer. The matching steel washer on the movable leg does not pivot and appears to be there for aesthetic reasons only. As the leg moves outwards, the tendency is for the point to lift from the drawing. To counteract this, the reversible pen/pencil insert is free to slide within the tube attached to the leg, thus keeping the point in contact with the paper by gravity.

I was pleasantly surprised by how easy it was to draw a perfect oval, provided the compass was held vertically and turned with a smooth action. Of course, due to the offset of the drawing leg from the template, it would never be a true ellipse, but the shape of the template seems designed to compensate for this limitation. This modification is particularly noticeable at the narrow end, where the extremities are “pointier” than an ellipse, but the resulting drawn ellipse is consequently much closer to its intended form.

Baraban Taguel elliptical compass test

In comparing the narrowest oval that can be drawn with the compass against standard modern ellipse templates, its dimensions closely resemble a true ellipse of approximately 30 degrees projection. This again would seem to be by design, intended to strike a compromise between maintaining a reasonable approximation to a true ellipse whilst offering the greatest useful range (including isometric ellipses at 35 degrees 16 minutes). It becomes evident in using the compass that its mechanism effectively precludes anything narrower than 30 degrees or smaller than 3 cm major axis, a limitation often found in other designs of ellipsograph.

All in all, the Baraban/Taguel elliptical compass is an interesting variation on the type, particularly for its extreme ease of use, but perhaps fundamentally flawed in its imperfect geometry.

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