Measuring Rules

Of the early history of this manufacture it may be sufficient to state that until the early part of the seventeenth century, at which time Edward Gunter invented the line of logarithms graduated upon a sliding scale, which solves problems instrumentally in the same manner as logarithms do arithmetically, the trade never assumed sufficient importance to cause it to be followed by persons who had no other occupation, and to make it worthy of being designated a craft.

Up to that time the best measures had been made by the mathematical instrument makers; but this ingenious invention of Gunter, by reason of its universal applicability to measuring purposes, called into existence another class of workmen, superior to those who had hitherto chiefly made the notched sticks similar to those used in many rural districts at the present day, but still somewhat distinct from the opticians and makers of such instruments as quadrants, sextants, and the finer kind of optical and mathematical instruments. The first men who were worthy of the name of rule-makers were to be found only in London; but after a time the trade gradually extended itself to Wolverhampton and Birmingham.

Under date of the 10th of August, 1664, Mr. Pepys records in his diary his experience of the scarcity of competent rule-finishers (as the men who make the rules are called) in London. He writes:—

“Abroad to find out one to engrave my tables upon my new sliding rule with silver plates, it being so small that Browne, that made it, cannot get one to do it. So I got Cocker, (the celebrated arithmetician and) famous writing-master, to do it, and I sat an hour by him to see him design it all; and strange it is to see him, with his natural eyes, to cut so small at his first designing it, and read it all over, without any missing, when for my life I could not, with my best skill, read one word or letter of it.”

And then on the next day Pepys writes :—

“Comes Cocker, with my rule, which he hath engraved to admiration, for goodness and smallness of work; it cost me 14s. the doing.”

From the fact that Browne, the mathematical instrument maker, was unable to find anyone to engrave Mr. Pepys’s sliding rule, it is to be supposed that the art had not then attained to much perfection, or rather that proficiency in it had been made but by few. In 1755, nearly a century later, is recorded that even in London “it was a most difficult matter to get rules good, there being only one man who could make them perfectly well, and he had lately taken to other work.”

In July, 1755, James Watt found his first employment in London as a rule-maker, under Mr. John Morgan, of Finch-lane, Cornhill, of whom Watt writes to his father, that “though he works chiefly in the brass way, yet he can teach me most branches of the business, such as rules, scales, quadrants,” &c. In less than two months after his arrival in London Watt says he had made a brass parallel rule eighteen inches long, “and a brass scale of the same length.” By December he “could work tolerably well,” and “he expected that by April he would understand so much of his business as to be able to work for himself.”

When June had again come round, and within twelve months of his first attempt at rule-making, Watt wrote to his father, that “he could now make a brass sector with a French joint, which is reckoned as nice a piece of framing-work as is in the trade.” Watt, however, having doubtless acquired proficiency in the art of rule-making, did not “work for himself,” as it appears he intended to do, but turned his attention to the improvement of the steam engine, and thus conferred greater benefits upon the world than he would, had he continued the manufacture of “parallel rules,” or even “sectors with French joints.”

It may be interesting to know that the sliding rule, long used by James Watt, is still preserved in Birmingham, in the possession of an eminent founder; and it is still used as a check in testing calculations. Is it not probable that this rule may be the handiwork of its former great and famous possessor?

Five and twenty years later the finer kind of measures were still made in London by the instrument makers; but the more ordinary kinds of carpenter’s rules were manufactured almost exclusively in Wolverhampton. At the latter part of the past century only three or four rule masters, each employing a few apprentices and men, were to be found in Birmingham, and one at Harborne adjacent; but now the trade has almost deserted Wolverhampton, which numbers only four or five persons employed in it, while Birmingham affords employment to as many hundreds. With the exception of three or four makers scattered throughout the country the trade is now entirely confined to Birmingham and London.

Many of the rules sold as London-made are produced in Birmingham, and many are framed in Birmingham and sold to the London makers, who mark or finish them themselves. The joints of the earliest made rules were cut from the wooden pieces which formed the legs, and brass plates were attached to the outside to strengthen the otherwise weak and wooden joints. Afterwards the joints were composed of metal, and attached to the wooden sides, instead of being made out of them.

The joint, so well-known as the arch-joint, and which is seen upon so great a number of joiners’, and other rules, was first made about sixty years ago; yet in a celebrated modern painting representing the early printers at their labours in Westminster Abbey, we find an accurate representation of a two-feet rule with this kind of arched joint, the artist being unaware that it was not invented till more than 300 years after those early printers had distributed their last form.

The general shape of rules has been but little varied, the convenient arrangement of two or four legs having been early introduced. Seventy years ago, the ordinary thickness of the boxwood carpenter’s rule was not less than a quarter of an inch, but that size has been gradually reduced from time to time in order to give greater flexibility. Many rules have been made of only the sixteenth of an inch in thickness, this small size of wood having to be further cut away to admit of the insertion of the joint, which is inlaid so as to lie level with the surface of the wood.

To remove this weakness of the joint, which was the common fault of all thin rules, a joint was produced by Messrs. John Rabone & Son, which being rivetted upon the surface of the boxwood legs instead of any portion of them being cut away to make place for it, adds strength to that part of the rule which had formerly been the weakest. These joints are also enriched by many artistic and ornamental designs stamped upon them, which render the rules, whether regarded for the greatest strength combined with extreme thinness, or for their elegant appearance, appropriately designated by the appellation of “nonpareil.”

The processes of sawing, rivetting, filing, and planing, are too well known to need reference here; but the numbering and graduation of rules is an operation which, to those unacquainted with it, is generally regarded as the most interesting of the processes. Since the invention of the dividing engine by Ramsden, and its improvement by Troughton, Adie, Reichenbach, Gambey, and others, all the most accurately and finely graduated astronomical and other instruments have been divided and marked by means of it; but the process is much too slow and costly to be employed upon the rules in general use by mechanics.

Straight scales and rules are usually divided by placing the article to be divided and the original pattern side by side, then passing a straight-edge with a shoulder fixed at right angles to serve as a guide, along the original, and pausing at each division; then a corresponding line is made on the copy by the dividing knife. Segments of circles are also graduated in the same way, by making a straight-edge revolve on the centre of the circle, and marking off the divisions as on the straight scale. This method, in skilful hands, admits of much accuracy, and was applied to the graduation of theodolites and other instruments prior to the invention of the dividing engine.

About eighty years ago much labour was spent by a Wolverhampton rule maker in the construction of a pair of steel rolls, having upon their surfaces in relief, the various lines, divisions, and figures necessary to impress, at one operation, the two sides of a scale or rule. Its costliness may be guessed at, when it is stated that the scale it was intended to impress contains 2205 lines, divisions, and figures. But the attempt was, as might have been supposed, a failure.

Owing to the inequality in the density of the wood, and the slight unevennesses of its surface, the work performed by it was defective, and its use was abandoned. Marking by pressure produces a thick, shallow, and ill-defined line; whereas percussion, when applied to the steel stamps which bear the figures or letters, gives a sharp, clear, deep and lasting impression. The filling up of the marks on the rules is easily effected by simply smearing over them a mixture of oil and charcoal, and wiping the surface clean.

In the year 1858, the late Dr. William Church, of this town, invented and patented a number of machines for the making and graduating of rules. These inventions displayed a vast amount of thought and ingenuity; but he was unaware of what had been done by a few persons in the trade before, and unfortunately for him all that was good and practicable in his inventions had been in use for many years, and his marking apparatus was too complicated ever to remain long in working order.

And when it is known that the 540 divisions in the Gunter’s line which may be seen on the brass slide of any carpenter’s slide rule, are cut singly and accurately by hand in ten minutes by the process above described, it will not be surprising that in this instance manual labour should be cheaper and more to be relied on than machinery, designed as Dr. Church’s was, to draw all those divisions at a single operation. In the working of several hundred teeth or cutters all connected together, the blunting or breaking of any one of them would render the work imperfect, and would consume more time in the filing up than the entire process, when performed by the usual method.

The box-wood, of which rules are made, is chiefly grown in Turkey, the English grown box-wood not being of sufficient size and quality. Formerly, large quantities of rules were exported to the United States of America; but, during the past thirty years, they have been manufactured in the States, a prohibitive tariff having prevented the introduction of English made goods.

The way in which some nations—or rather— some Governments—regard the importation of rules into their territories is rather strange. Some allow, at fair and equitable rates of duty, the importation of English made rules, the measures being suitable to the use of their respective countries. But while one country will not admit them at all, unless the measure of the country is surrounded by other measures, so as to make the rule a scale of varied measures, instead of being only the legal standard of the country; another Government looks upon all rules, coming to its ports as illegal measures, because they have not the Government stamp upon them, and all so found are seized.

The makers do not put a resemblance of the official stamp upon them; and, as there are no native rule makers, and all the rules are imported, measures, a little different from the legal standard are made, and being marked with the name of another country than that for which their use is intended, are allowed to be admitted; thus, the greater part of the people are necessarily using an incorrect measure, at the same time that the true standard might be supplied to them as cheaply and more readily.

The various counties and states of the world have, at the present time, about 150 different measures; many small places, each containing only a few thousand inhabitants, have their own peculiar measures. At various times, many of these measures have been changed from the duodecimal to the decimal division, still retaining the original standard of length; but, within the past few years, the use of the French metrical measure has become much more common in all parts of the world. Many nations, now, have a large proportion of their rules marked with the French metre, in addition to their own standard; and are thus, doubtless, gradually tending to the general adoption of so convenient and perfect a measure of length as the French metre is admitted to be.

J. Rabone, Jun.

The Resources, Products, and Industrial History of Birmingham, and the Midland Hardware District: A series of reports, collected by the local industries committee of the British Association at Birmingham, in 1865.

—Jeff Burks