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Stanley’s first planimeter (part 2)

My last post ended with a slew of questions that I had intended to address in a second instalment, but as I began to assemble the evidence it quickly became clear that each question had ballooned into an entire post in its own right. For this reason today’s post will delve into the first of these, namely who made Stanley’s mystery planimeter and when.

We have already established that this was the very instrument that appeared in the 1868 third edition of Stanley’s Mathematical Drawing Instruments, so it must already have existed before that date. (The first edition of 1866 is a whole different story, but one that must wait until later for reasons that shall become clear.)

At one level, provenance doesn’t get more concrete than this, being able to pin down a specific instrument to a precise time and place. Yet in the absence of other documentary evidence, the origins of this otherwise unremarkable polar planimeter and the purpose for which it was made still remain unclear.

For this reason, I went back to the instrument itself in the hope of discovering further clues. First of all, and perhaps most significantly, the planimeter was evidently handmade. All of the text or numbering is manually engraved, with no use of stamps or pantographic engraving anywhere on the instrument (even the earliest examples of Amsler’s work were marked with stamped serials). The graduations on the roller and vernier are also hand cut, but with the extreme accuracy that tends to characterise the work of professional instrument makers.

Stanley 1860s polar planimeter zero arrow symbol on vernier

Furthermore, there are several signs that it may have been a one-off or experimental model:

  • Adjacent to the counter spindle bearing there is what appears to be a misdrilled pilot hole
  • Scribed construction lines can be seen on the metal surfaces, for example an alignment mark for the needle holder assembly
  • A loose piece can be heard sliding inside the hollow pole arm tube, presumably a metal fragment that was unintentionally sealed in during fabrication
Stanley 1860s polar planimeter misdrilled pilot hole for indicator disc

Even so, its close resemblance to an Amsler planimeter means that it was clearly based on one or more sources – whether instruments or drawings – that were directly derived from the original patented design. By extension, every aspect of the instrument (other than mistakes, as mentioned above) must have resulted from a conscious choice to either adopt or reject the structures present in polar planimeters that existed at the time.

Stanley 1860s polar planimeter scribed alignment mark for needle assembly

Therefore, by assessing the constructional details as if it were an Amsler-made planimeter, it should be possible to form an idea of where the model(s) for the Stanley-signed copy would sit chronologically, and therefore the earliest possible date that it could have been made. This task has been greatly assisted by the invaluable archive of early Amsler images on David Green’s uraone website, along with some of the discussions that have taken place in the Drawing Instruments group.

As has been pointed out elsewhere, the basic design of Amsler’s polar planimeter remained essentially unchanged for over a century. The modifications that did occur during this time tended to be persistent – once established, they would remain the same from that point onwards – which helpfully allows instruments to be arranged chronologically with relative ease. On Amsler models this can be validated by reference to serial numbers, but since all polar planimeters are more or less distant descendants of the archetypal design, the same details can often be used to give an approximate earliest date for other manufacturers’ instruments.

For example, the earliest known Amsler model to include a pole weight was serial number 543, after which it was supplied with all types 1 to 4 (but not the pantographic type 5 with its heavier construction until some time later). These weights were remarkably consistent dimensionally, having a diameter of almost exactly 20.9 mm and a height of around 10 mm. However, a few of the earliest weights appear to have been somewhat shorter, particularly noticeable on serial number 543. The height visibly increases through number 569 (and therefore the mass, assuming the diameter to remain constant) until by number 582 the weight appears to be of the later taller variety.

A similar early divergence can be seen in the diameter of the indicator disc, which is consistently 15 mm for later examples, but only 14 mm on my number 2125 (the lower planimeter in the image below) and even smaller on numbers 5 and 213.

Early Stanley brass polar planimeter counter compared with serial no 2125

Another obvious difference in the earlier models was the use of a circular section rod for the pole arm, present until at least serial number 582. From 1064 onward, both arms were fabricated from the same square section rod.

Clearly the Stanley model has both a pole weight and a square section pole arm, so it must postdate Amsler’s number 582, which still had a round pole arm. It also has a micrometer adjustment, the first known appearance of which was on serial 1064, but was not yet present on 582 which featured a simple clamping screw.

Turning to the weight, I measured the Stanley example with a one inch micrometer and found the diameter to be 0.8034″ (20.41 mm) and the height 0.3187″ (8.09 mm). This diameter almost matches Amsler’s, being slightly smaller (and very nearly 0.8 of an inch which may suggest it was machined to imperial units). However, the height is almost 2 mm less than the later standard, much closer to the early Amsler weight heights.

Early Stanley brass polar planimeter pole weight compared with serial no 2125

The same is true of the indicator disc, which measures to 0.5765 in diameter (14.64 mm), smaller than the very consistent 15 mm of later Amsler models. The cross section of the square pole arm and tracer arm is fairly consistent, averaging 0.202″ (5.13 mm), just slightly more than Amsler’s 5 mm and again suggesting an imperial units “best fit” at 0.2 inch.

These measurements lean towards a model for the Stanley instrument that predates Amsler’s serial number 1064, an idea that is reinforced by further differences in detail. Stanley’s needle point holder is shaped much more like those of Amsler’s 213 and 569, with a longer taper rounded at the end that contrasts sharply with the later conical holder. It also lacks the kick-out projection on the bracket directly behind the vernier, a feature that appears on all Amslers after serial number 1064 but is universally absent from 582 and earlier. Finally, there is an additional screw under the pole arm pivot that appears on Amsler 1064, but not on 582 or prior examples.

Early Stanley brass polar planimeter end detail lacking kick-out

While this may seem like a lot of unnecessary detail, it provides several positive datum points to which the undated Stanley instrument can be reliably fixed. Taken together, they suggest Stanley referred to a model that was produced between serial numbers 582 and 1064, representing a date range of 1856-57, some ten years before it appeared in Stanley’s book.

Of course, this does not mean that it was made at this time – although it might have been – only that the model for Stanley’s planimeter was overwhelmingly likely to have come from this time period.

However, there is a piece of circumstantial evidence that supports this earlier date. On first seeing Stanley’s address on the pole arm, it immediately struck me that the London postal district code “W.C.” (West Central) looked out of keeping with the rest of the lettering.

Stanley 1860s polar planimeter different engraving style of W.C.

At first I had imagined this might be for stylistic reasons, similar to the way that the street directories of the time sometimes printed the district codes in small capitals. Looking more closely, this does not seem to be the case. The spacing between “Holborn” and “W.C.” is much tighter than the rest of the engraving, as if the flow had been broken. Under 20x magnification it can be seen that the cuts are wider and deeper, particularly obvious when comparing the dots, as might be expected if a different tool had been used (note also the very faintly scratched guidelines for the letter positions that are just visible).

If, as this suggests, the W.C. designation was added later, why might this have been? London’s postal districts were first devised in 1856, but only came into use gradually during 1857 until the scheme’s completion on 1 January 1858. These dates align neatly with the first use of the W.C. district code in Stanley’s advertisements of the time. The earliest to feature the new postal district appeared on 9 January 1858 in The Builder, although an earlier letter to The Engineer about the Isogon square dated 25 May 1857 was also signed with the new address format, which suggests that Stanley was an enthusiastic early adopter.

It is therefore not inconceivable that the Stanley planimeter had originally been signed with the address ending in Holborn (itself unusual, as most if not all of Stanley’s instruments for sale were explicitly marked as London made), with the W.C. added some time during 1857 or early 1858 when the new system came into general use. This would fit with the planimeter being made in 1856-57 as indicated by the its features, and lends weight to the idea that Stanley was copying the current Amsler model, rather than one that was more than a decade old as it would have been by the time the third edition of his book went to press. Peculiarly English features such as the arrow used for the zero mark on the vernier, along with the non-metric sizing of its parts mentioned earlier, indicate that it was domestically made. The maker may even have been Stanley or one of the workmen directly under his supervision (remember that in 1857 Stanley was 32 years old and had only been in business for three years, so most likely still relied heavily on outworkers for anything he did not make himself).

Quite why Stanley would want or need to make a copy of this new instrument is another matter. Clearly, the fact that Elliott Bros had sole agency and that Amsler’s planimeter design was protected by a British patent meant that it was impossible for Stanley to sell a competing model. Indeed, Stanley’s advertisements of the time show that he had only just begun to sell metal drawing instruments in 1856, at which point the business was still known as Stanley & Robinson.

Stanley and Robinson advertisement in The Builder 19 April 1856

On the other hand, as an instrument maker himself, he may have been interested in the economics of these Swiss imports, much as the early success of his business has been attributed to Stanley being motivated by his father’s observations about cheap imported drawing instruments.

Equally, he may simply have wanted the challenge of making a working copy of this deceptively straightforward design. If that was the case, Stanley may soon have found out just how wrong he could be.

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