You are currently viewing The Armstrong scale: a hypothesis

The Armstrong scale: a hypothesis

Among the more ubiquitous instruments named after their inventors – from Captain Field’s parallel to the Napier compass, Gunter’s chain to Marquois’ triangles – arguably the most widely-known and numerous must be the Armstrong scale.

I had never given much thought to the origin of this particular type of scale, which generally takes the form of an oval section rule with eight open-divided scales, two to each edge, ranging from 1/8 to 3 inches. Armstrong scales were made from six to eighteen inches long, with the former being the most common. These were especially popular as promotional items, usually emblazoned with a company’s name and contact details down the middle of each side, to be distributed as gifts to clients.

Promotional Armstrong scale

If you had asked me to guess which Armstrong these scales were named after, I would probably have suggested the Victorian industrialist Sir William Armstrong, already known for his improved version of the two-fold sliding carpenter’s rule, as described in the booklet The Carpenter’s Slide Rule: Its History and Use published by Rabone & Sons who also manufactured the rule.

It was only a chance acquisition that finally prompted me to investigate further. The story begins, as it so often does, with a job lot of scale rules that I purchased semi-accidentally on ebay (please don’t ask how it is even possible to semi-accidentally buy a dozen rulers). On checking the photos to determine what I had just unwittingly parted with the sum of four pounds and thirty-nine pence for, nothing particularly stood out.

Job lot of scales including R&J Beck

The only item that seemed remotely interesting was a plain boxwood rule with what at first I took to be a conventional open-divided Armstrong scale arrangement. The maker’s name and address were just visible in the pictures – R. & J. Beck. 68 Cornhill. London. – which narrowed down the rule’s date to between 1880 when Beck moved to 68 Cornhill and 1894 when they became a limited company, thereafter signing their instruments R & J Beck Ltd.

R&J Beck Finsbury Technical College Scale obverse detail

None of this seemed particularly exceptional – Beck’s main business was in microscopes which made it seem unlikely that they were the actual fabricator of the rule – so I was not expecting much of any interest from the lot. A few days later the rules arrived, all rattling around in a padded bag with one end torn open and patched up with Royal Mail “Damaged” tape. Fortunately (if that’s the right word) the rulers seemed largely unscathed by their ordeal, so I quickly checked them over with the expectation that they would all end up in my spares box.

The Beck scale was broadly as it had appeared in the photo, with a few ink stains, scratches and a couple of tiny chips, but otherwise acceptable for its age. However, when I turned it over to examine the back I was intrigued to discover that the ruler had a name, but disappointed that this had been partially scratched out at some point. The two legible words were “Technical” and “Scale”, but the first and third words of the name were almost entirely obliterated. With a magnifying glass I could just make out that the third word was “College”, so it was a something Technical College Scale.

R&J Beck Finsbury Technical College Scale reverse detail

The first word was harder to read, but seemed to begin with an F, end with a Y, with UR in the middle. With the aid of the internet and a field microscope, I finally worked out that the missing word was “Finsbury”. Finsbury Technical College is generally recognised as the first technical college to have been established in England, formally opening for day students in 1883. It was considered a “Model Trade School” and served as a prototype for the numerous technical schools and institutions in Britain that were to follow.

While this backstory made the rule marginally more interesting, it was fairly commonplace for Victorian-era educational establishments to require students to buy specific equipment from their own in-house shop (I have various examples made for Imperial College Bookstore, Eton School and so on). It also made sense of the scales, which were the kind of general purpose ones that might be needed by a trainee engineer or the like.

R&J Beck Finsbury Technical College Scale both sides

This made me wonder if the missing words had been erased by a former student who had graduated from (or flunked out of) Finsbury Technical College, but perhaps continued to use the rule in their workplace and did not want to be seen with a branded college rule, but was fine with a “Technical Scale”. It would certainly have served the same purpose as an Armstrong scale, from which it differed primarily by the duplication of the inch and quarter inch scale on the reverse, divided by tenths rather than the usual duodecimal divisions. This came at the expense of the half inch scale, which is absent from the rule, while one edge is shared by the standard inch, 1/4 and 1/8 scales.

R&J Beck Finsbury Technical College Scale end details

I assumed that these variations must have been made to suit a particular aspect of the syllabus at Finsbury Technical College, as the loss of the half inch scale and the cluttering of one edge with three scales seemed to compromise the usability of an otherwise perfectly good rule. With this in mind, I began to look into the history of the first technical college and its objectives, in the hope of finding some clues. It was at this point that I stumbled upon the names of the founding professors: William Ayrton, John Perry and Henry Armstrong.

Improbable as it seemed that this Professor Armstrong was in any way connected with the Armstrong scale, I nevertheless decided to investigate. Henry Edward Armstrong was a renowned chemist who even had a fluorescent acid named after him, a seemingly unlikely candidate for a scale rule designer. However, this was only one side of his professional life. Armstrong was also a pioneering educationalist, dedicated to improving schools by the application of scientific method to all areas of study. Two decades of his thoughts on the subject are collected in the book The teaching of scientific method and other papers on education published in 1910.

Armstrong was a pioneer of the “heuristic” method – learning by doing – that was underpinned by observation and measurement, so unsurprisingly he had strong opinions on rulers, which feature prominently throughout his writings. He also championed the metric system as essential to efficient scientific practice, and the two themes can be seen together in his recommendations for the equipping of school laboratories, in which:

“… there are certain articles which must be provided — notably centimetre-foot-rules, drawing-boards, T and set squares and balances. The best rule to provide is one made of steel, graduated on one face to millimetres and centimetres on the one edge and to inches on the other; if the inches are subdivided into twelfths, an opportunity is afforded of contrasting decimals with duodecimals. It is advisable to have the rule graduated on its second face into inches and tenths and lower decimals and subdivisions on the one edge, and into inches and 16ths, 32nds, etc., on the other. Such a rule is a perpetual object lesson; its possessor cannot help visualising twelve inches and thirty and a half centimetres as practically equivalent lengths.”

He advocated a similar approach for even the very youngest age groups, with the suggestion that:

“The measurement lessons in the first instance may be of the simplest kind. Much may be done with the aid of a boxwood scale divided into tenths of an inch on the one edge and into millimetres on the other; with the aid of such a scale, children may learn to measure accurately and may be taught the use of decimals and the relation between the English and the metric system.”

It is clear that Armstrong regarded it as a matter of the greatest importance that imperial and metric measures should be seen side by side, if only that:

“… the irrationality of the English system may then be explained.”

With such strength of feeling, it is inconceivable that Armstrong did not offer at least some input to the equipment used in the technical school that he had founded. Indeed, just ahead of its opening the Journal Nature stated:

“The fittings of the new College, which are most complete and admirably adapted for practical teaching, have been designed and executed under the direction of Professors Armstrong, Ayrton, and Perry.”

It would certainly explain the priority given to decimal divisions on the Finsbury Technical College Scale, even if the metric system itself was considered a step too far in practice. As a chemist with a particular interest in crystallography and the structures of molecules, Henry Armstrong’s involvement would also make sense of why Finsbury Technical College had gone to a microscope maker for their scales, rather than one of the more established drawing instrument suppliers.

So how does all this relate to the Armstrong scale as we know it? WF Stanley had been selling open-divided oval-section rules with the eight classic Armstrong scales since at least 1865, and W H Harling by 1883. In contrast, the Finsbury example lacks a half inch scale and crams three duodecimal scales onto a single edge. How was it possible that Armstrong’s name might have become attached to a rationalised version of the Finsbury scale that had already existed for two decades or longer? Enter another of the founding fathers of the technical college, John Perry.

Perry was a polymath engineer, scientist and mathematician who had worked as Lord Kelvin’s assistant in Glasgow before moving to Tokyo where he taught alongside future Finsbury co-founder William Ayrton at the Imperial College of Engineering (incidentally, Perry and Ayrton also collaborated on the design of what many regard as the first road-going electric vehicle).

However, it is Perry’s relationship with a well-known name in the world of mathematical instrument making that concerns us here: Alexander George Thornton. Thornton had championed Perry’s design for a revolutionary slide rule, the “System Perry” patented in 1901.

AG Thornton Improved System Perry slide rule

More significantly, Thornton had made modifications to Perry’s original design which he then sold as the Improved Perry Slide Rule from around 1904. Thornton’s catalogue description of this slide rule claimed that:

“Much thought and time was expended, and many rules were made and divided before the present rule was finally adopted by Professor Perry; indeed we introduced on the market a previous “Perry” rule with scales differently arranged, that is why the present rule is known as the “Improved Perry Rule”.”

If Thornton had collaborated with Perry in this way, is it possible that he had also established a working relationship with his colleague Armstrong? Schools and colleges were a key market for Thornton: the back of an 1887 catalogue offers “Every Requisite for the Drawing Office of the Engineer, Architect, Surveyor, also for Schools, &c.” and his c.1904 book Mathematical Drawing Instruments makes frequent reference to the needs of students and the suggestions of their professors (indeed, this begs the question as to whether Harling’s 1889 move from Hatton Garden to Finsbury Pavement was similarly in response to London’s shifting technological and educational centre of gravity).

Equally, it would not have been out of character for Thornton to take an existing design – in this case Armstrong’s Finsbury scale – and adapt it to meet the needs of a wider market, while trading on the credentials of its inventor. It may also be no coincidence that Thornton’s book contains one of the earliest descriptions of the Armstrong scale, although he does not elaborate on the origin of its name, nor claim any involvement in the design:

“Oval Section Scale.–The oval section, as above illustrated, is the most popular form, as it has the advantage from its shape of admitting a number of scales being cut on it and all read to the edge, and the one of these series in most general demand is called the Armstrong, and is illustrated above. There are eight scales marked on these, viz., 1/8, 1/4, 1/2, 1, 3/8, 3/4, 1 1/2, and 3 in., each scale is open divided, and sub-divided at each end. This form is a very useful arrangement (for engineers particularly).”

The connections do not end there. Archibald Low, who studied under both Perry and Armstrong, invented a flexible curve that was made and sold by Thornton as the Low Flexible and Adjustable Curve. Once again, this hints at connections between the two professors and Thornton that extended beyond the System Perry slide rule.

Of course, all of this evidence falls short of definitive proof that the Armstrong scale was named after the Finsbury professor. Equally, the evidence for Thornton’s involvement is at best circumstantial, particularly in the absence of early catalogues that might shed light on when he began to sell scales under the Armstrong name. However, to my mind there is one final compelling piece of evidence that brings our story of the Armstrong scale back to Finsbury Technical College. It can be found in volume III of A Dictionary of Applied Physics published in 1923, under the section on draughting devices (my emphasis below):

“A special scale (see Fig. 23) known as the “Armstrong,” for use in technical schools and colleges, is made oval in section. The four edges contain “eight scales,” viz. 1/8, 1/4, 1/2, and 1 inch to the foot, 3/8, 3/4, 1 1/2, and 3 inches to the foot, and the scales are open divided and subdivided at each end as shown.”

While secondary sources of this kind can often be inaccurate or derivative, the authority of this particular piece is unimpeachable. The contributor of the section on draughting devices is revealed to be Alma Turner, A.M.I.Mech.E., who worked for the National Physical Laboratories (NPL) in the Metrology department and was the holder of numerous patents for high-precision measuring devices. This was someone who clearly knew a thing or two about scales!

Armstrong scale from A Dictionary of Applied Physics

It also brings into focus what, in a sense, was obvious all along: that while professionals could have aspired to a handsome set of rules, with the convenience of a single scale to each rule, this was beyond the means of the young student in training for these professions. The Armstrong layout provided all the necessary scales in a single rule that was both compact and affordable.

It is perhaps unsurprising that many of these future professionals should have taken their Armstrong scales with them into the office, eschewing the cumbersome mahogany-cased status symbols of their forebears. In a way, this perfectly encapsulates Henry Armstrong’s ambition to raise a new generation of practical, empirically-minded individuals who he saw as vital to the progress of humanity. In Armstrong’s own words, from the preface to his collected essays:

“While the classes which formerly stood out as cultured are falling behind, a new intellectual order is arising, comprising the workers in various branches of science and engineers – men of deeds rather than of words, who are all striving to go forward and to give peace to society, true missionaries in the cause of progress. However much their work may be delayed by ignorance, they will eventually conquer, as they have no selfish ends and are bent on bringing mankind into intimate touch with nature.”

Is it possible that Armstrong’s greatest contribution to this goal was a humble ruler that found its way into the hands of millions?

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