November 16th 2023 marks the bicentenary of Jakob Amsler-Laffon’s birth – at least according to the more trustworthy sources – so it seemed only fitting to save a rather special planimeter for the occasion.
Conveniently, this post begins where the last one finished, with WF Stanley’s introduction of the homegrown “Allbrit” planimeter range in the early 1930s. The significance of this moment was not lost on the author of Stanley’s 1953 jubilee publication, A Century of Scientific Instrument Making, who asserted:
“This ingenious instrument for the measurement of areas originated in Switzerland in the 1850’s, and it was some 80 years later that Stanleys first began its manufacture in Great Britain.”
Of course, planimeters signed by British makers had been sold ever since Elliott Bros first exhibited Amsler’s patented instrument at the ninth Society of Arts exhibition in 1857. Over the following decades, Elliotts were joined by the likes of Stanley, Davis & Son, Halden, Thornton and countless others who listed a range of polar planimeters in their catalogues. However, behind these familiar names the reality was quite different, as explained by Professor O. Henrici, F.R.S., in his 1894 “Report on Planimeters” to the British Association:
“Many thousands of them have been manufactured by Amsler at his works in Schaffhausen, and though in England many are sold with the name of an English firm engraved on them, practically all have come from Schaffhausen.”
Even those few that did not originate with Amsler were imports, mostly from a handful of German makers who had commenced production in the 1860s as the patent period came to an end.
This was the backdrop to my purchase of what seemed, to all intents and purposes, an ordinary Type 3 polar planimeter signed by WF Stanley. The most obviously unusual thing about it was the box.
From the outset, most Amsler planimeters sold in England were supplied in the same leather clad, velvet lined cases as their Swiss counterparts, readily identifiable – and to a certain extent dateable – by the consistency of their details over time.
In contrast, this planimeter was housed in a mahogany box, similar to those used by Stanley for surveying equipment, protractors and the like. While Amsler’s planimeters were held snugly in a fitted recess, this one was supported on a pair of simple mahogany blocks, only the top edges of which were covered with blue velvet strips. Likewise, the pole weight was held sideways by a separate block, not face down in a circular recess like Amsler’s.
On the other hand, the box had no manufacturer markings, so my initial thoughts were that it might have been a replacement for the original Amsler-type case. And this is where my interest may have ended, had I not looked more closely at the planimeter itself.
The hand-engraved W.F. Stanley address marked it out as a potentially early example, but not especially so – I have seen similar engraving on other Stanley-supplied Amslers, for example serial number 17,589 below.
More puzzling was the use of hand engraving for the scale numbering, a practice that had been phased out on Amsler’s instruments by the mid-2000s serials. Significantly, this was well within the sole agency period of Elliott Bros, which is said to have ended in 1868, making it all the more incongruous on a Stanley-signed instrument.
Upon closer inspection, even stranger things were afoot. Most obvious was the connection between the tracer arm and the steel pin. On Amsler’s planimeters, this connecting piece had evolved from a tapered prism connected to a cylinder (as seen in the patent drawings), to a more organic element in which a downward-curved rectangular section merges seamlessly into the cylindrical point holder. An altogether more rudimentary piece does the job on the Stanley planimeter – a flat U-shaped piece of brass that has an almost unfinished look, the tracing pin unceremoniously punched through its blocky end – and lacking in any of Amsler’s elegant refinements.
A similarly angular form is found on the clamp for the micrometer adjustment, a feature that had been introduced by Amsler around serial number 1000, but with a much more rounded profile.
On the Stanley version both brackets are made of bronzed brass, further accentuating the difference with Amsler’s uniform lacquered metal finish. The armature that supports the indicator disc is also simplified, its underside completely flat in contrast to the more or less elaborate stepped detail that is found on practically all Amsler instruments (excepting those few around the 500s with elegantly-curved brackets).
A notch cut out of the top face of the tracer arm mounting is of unclear purpose; it looks like it should be the index to which the scale marks are aligned, as seen on Amsler’s patent drawings and earliest models, but the scale marks are on the side of the Stanley tracer arm.
Likewise, the tension springs from which Amsler’s index is conveniently formed have been moved to the back of the Stanley model, making the cutout notch feel almost like a vestigial hangover.
In short, everything felt a little “off”, but most glaring of all was the absence of something that reliably appears on every Amsler instrument from the very beginning: a serial number. This seemed to confirm that the Stanley planimeter was not made in Schaffhausen, but comparisons with the instruments of other known makers (Blankenburg, Dennert & Pape, Haff) were equally fruitless.
Still, there was something about this oddly shaped but obviously precision-made polar planimeter that looked somehow familiar, and the answer turned out to be very close at hand. In the chapter on computing scales from Stanley’s book Mathematical Drawing Instruments there is a short description of the planimeter accompanied by an engraving made specially for the book, as most of the illustrations were, by Thomas P. Collings of 38 Surrey Street, London.
Had I given this image more than a cursory glance in the past, I might have assumed it was the result of artistic licence, or else the naive oversimplification of an inexperienced apprentice engraver. It may even have occurred to me that unlike Elliott Bros who, as official agents, had access to Amsler’s original illustrations for their marketing material, Stanley was obliged to procure his own visual material. Now it became clear that Collings’ engraving was accurate to the last detail, from the tracer to the micrometer and even the mystery notch on top.
If it came as a surprise that the illustration was based on an actual instrument, and one apparently not made by Amsler to boot, an even bigger surprise was waiting in Stanley’s accompanying text. After listing the scales marked on the planimeter “as supplied by the patentee from Switzerland” (which also happen to match those on the Stanley instrument), he adds:
“Besides the above, there are numbers engraved along the top of the bar, which vary slightly with the construction of the instrument. In the one before the writer they are 20.781, 20.769, and 22.065.”
These constants, used to calculate the true area when the pole is placed within the figure, are essentially unique to each planimeter. They were derived by an individual calibration process and subsequently engraved on the instrument adjacent to the relevant scale marks, or sometimes (in the case of single-unit planimeters) on the pole weight, as seen on serial number 2125 below.
The last two constants mentioned by Stanley can be clearly seen on Collings’ illustration, so the planimeter he describes in the text would appear to be the same one used as a model for the illustration.
On my example, the top of the bar had not been visible in the auction photos, so it was with some trepidation that I removed the instrument from its box to check its numbers, like some kind of planimeter lottery. As improbable as it seems, all three were identical to those in the book. It could mean only one thing: not only did this strange instrument look just like Stanley’s planimeter, it was Stanley’s planimeter.
This revelation raised several questions. Who made the instrument and when? How did it end up in front of Stanley while writing his book? Why did he not use a standard Amsler-made planimeter for the engraving? And finally, by what circuitous route had it come into my possession? Clearly, more than a century and a half later, it may not be possible to find all the answers. However, a number of clues can be discerned in both the instrument itself and the wider context in which Stanley’s book was written, which I will save for the next post.