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It is a well-worn truism that nothing is certain except death and taxes, and certainly throughout history much effort has gone into making sure that the latter is as inescapable as the former. One of the earliest forms of taxation was the tithe (derived from the Old English word for a tenth), given as payment in kind to the church – that is, one tenth of the produce of the land such as crops, animals, timber, etc. – and stored in a dedicated “tithe barn” belonging to the parish.

Over time, the picture became more complex, with much church land having passed into private hands after the Reformation, along with the inherited entitlement to receive tithes. By the nineteenth century, the system was coming under strain, with widespread disputes culminating in the Irish Tithe War of 1831-36. It is probably no coincidence that in 1836 the British parliament passed the Tithe Act, intended to replace the old payments in kind with their monetary equivalent – colloquially known as a “corn rent” – based on the assessed value of the land. This resulted in the formation of the Tithe Commission, a body tasked with the production of maps of all areas that came under the new Act.

It was a huge undertaking, involving the production of surveys of much of the country to a uniform standard, the majority of which was done within the first five years of the commission’s existence, and mostly completed by 1851. At this blistering pace, it is perhaps unsurprising that shortcuts and discrepancies began to creep in, and ultimately only about one-sixth of the maps produced were of high enough quality to be “sealed”, or certified by the commissioners, the so-called “first class” maps.

The “second class” maps varied greatly in accuracy, drawn to a range of scales, with some little more than topographical sketches. Mired down in the seemingly endless task of calculating chargeable land areas from these disparate plans, it seems that someone at the Tithe Commission – probably one of the many human “computers” employed there – came up with an idea that would simplify and speed up the process. This instrument became known as the computing scale, one of the earliest references to which I have found in the second edition of A Treatise on Engineering Field Work (1840) by Peter Bruff.

The device Bruff describes as “now in operation at the Tithe Office” is of the simplest kind, consisting of “a box rule, with divisions at 2 1/2 chains apart” to which is attached a brass slider with a horsehair perpendicular to its length – literally a hairline cursor. It was used in conjunction with a piece of tracing paper laid over the plan to be measured, divided with parallel lines one chain apart, making each division on the rule equal to one rood. The cursor was subdivided on both edges into forty, making each subdivision a perch. An accompanying illustration shows the bidirectional layout of the scales which allowed continuous operation.

Computing scale from Bruff's "A Treatise on Engineering Field Work" (1840)

It is worth noting that the computing scale does not feature in the first edition of Bruff’s work published in 1838, which suggests that the innovation took place between the two dates. Even so, this was still when the Tithe Commission was in its infancy.

A development of the basic design appears five years later in the second edition of The Principles and Practice of Surveying (1845) by Charles Bourns, Surveyor, Member of the Institution of Civil Engineers. The author states that, “the best mode of casting contents is by a Computing Scale lately introduced”, described as a box ruler with a metal slide containing transparent horn and illustrated on p. 167. Following a description of the instrument’s operation (essentially as described in yesterday’s post), it is noted that:

The scale here described has been modified, in some respects, by Mr. Elliott, Optician, Holborn. I regret that I have been unable to ascertain who was the original inventor.

William Elliott had supplied the Tithe Commission with the highest quality electrum scales, so it comes as no surprise that he was also involved with the early computing scales. The fact that Bourns could not even discover the identity of its originator at the time suggests that it may remain a mystery.

Elliott computing scale from Bourns' "The Principles and Practice of Surveying" (1845)

The next development to emerge from the Tithe Commission is reported by WF Stanley in his Mathematical Drawing Instruments, and he spares no detail as regards the improvements introduced on the models produced by his firm.

The index line in some computers is drawn upon a piece of horn fitted in the frame; the horn becomes cloudy and cockled, which renders the plan beneath it very obscure. The author employed glass for the interior of the frame; this is also in some particulars objectionable. A gentleman connected with the Tithe Commission Office, where perhaps the greatest amount of computing is performed, has lately suggested to the writer the employment of a fine needle for the index line; this appears to answer better than the many previous experiments.

Beyond this tinkering with the cursor that had started with Elliott, Stanley goes on to describe a more significant modification which pertains to the instrument in my collection:

The writer has recently made for H.M. Tithe Commission Office a universal computing scale, the design of some of the gentlemen in the office. This computer is one in which the division is placed on a separate slip of boxwood. The slip slides into an undercut groove, and is read by an index. By this plan one computing frame only is used for as many scales as may be required.

Unfortunately Stanley does not say exactly when these changes were introduced – certainly before the publication of the third edition of his work in 1868. Some additional clues can be found in the firm’s early catalogues, the 1865 list offering:

Stanley’s improved Computing Scale [Boxwood] 0 18 0

However, by the time of the price list at the back of the 1868 edition of Mathematical Drawing Instruments, Stanley was selling both:

Computing scale, Stanley’s . . . . boxwood 0 18 0
” ” universal, T. C., with six scales . . 3 0 0

Therefore, it seems that the “improved” scale of 1865 refers to the modified cursor design, while the “universal” model was introduced later, some time between 1865 and 1868. At more than three times the price of the standard computing scale, this was an item aimed squarely at the top end of the professional market. Even taking into account the six scales provided with the set, it would have probably made more sense for the average user to buy a specific scale for the job, especially where two different scales were provided on the top and bottom halves.

Even so, it did not take long for other firms to get in on the act, the 1871 Casella catalogue containing:

UNIVERSAL COMPUTING SCALE, as used in H. M. Tithe Commission Office, containing 1, 2, 3, 4, 5, 6 chains to the inch, and 6 inches and 5 feet to the mile complete in mahogany case . . . . . £3 0 0
EXTRA SCALES made to the above . . . . 0 4 0

Harling, Thornton and others also sold their own versions of the universal type, the design remaining basically unchanged in their catalogues well into the 20th century. Quite how many were sold is another matter, given their expense and bulk, which may explain why they are seldom seen despite being manufactured for more than half a century.

WF Stanley Universal Computing Scale for the Tithe Commission with box

Turning to my example of Stanley’s Universal Computing Scale, it would appear to date from the first few years of production. The most obvious difference with other specimens I have seen is the inscription “STANLEY PATENTEE” on the body of the main boxwood scale. Inside the lid is the old-style yellow paper label with both the Great Turnstile and Railway Approach addresses, the latter having opened in 1867. The box itself is biscuit-jointed, which was superseded by comb-jointed corners after Stanley’s move to his new South Norwood works around 1875.

WF Stanley Universal Computing Scale for the Tithe Commission box corner

This gives a likely range of 1867 to 1875, a period of eight years. However, as Casella was already selling their own version of the universal scale by 1871, it is difficult to imagine that Stanley could have claimed patent protection after this date. Indeed, I have struggled to determine what precisely this patent marking refers to. Perhaps Stanley attempted to protect some features of the design, but was unable to secure a full patent for whatever reason (possibly a conflict with the Tithe Commission?)

WF Stanley Universal Computing Scale for the Tithe Commission box details

Other details worthy of note are the German silver end stops to each slide, which simplified the completion of each full measurement cycle. Adjacent to these stops, an inscription on each slide clearly states what type of tracing paper was to be used for each scale, for example “To compute with lines on paper 1/2 in apart” on the 1 chain scale. One or two slides also have faint pencil notes giving multiplication factors for other scales.

WF Stanley Universal Computing Scale for the Tithe Commission slides right-hand side

Stanley’s cursor has also developed into a complex piece of hardware, doing several jobs at once. It owes some of its design to slide rules, which Stanley was also involved in the production of. Each part of the cursor, frame and its slides are marked with an assembly number – in this case “4” – making it clear that these instruments were largely built by hand.

WF Stanley Universal Computing Scale for the Tithe Commission details

While the advertised universal computing scales came with six slides, my example has eight, filling the slots at the base of the box. My assumption is that the 1 to 6 chain scales were the standard six, while the two Ordnance Survey scales of 6 inches to a mile and 1/2500 were optional extras. Certainly by 1871 Casella was offering all eight scales as standard.

WF Stanley Universal Computing Scale for the Tithe Commission slides left-hand side

It is surprising to me that long after the Tithe Commission had wound up most of its operations, the market for these devices continued to the extent that other inventors entered the field with their own innovations. Perhaps some of these – including Merrett’s Patent Improved Computation Scale, Mavitta’s Comparative Drawing Scale and the Williams Proportional Plotting Scale among others – will be the subject of future posts.

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