This paper was originally published in the Slide Rule Gazette, Issue 18, Autumn 2017 by the UK Slide Rule Circle.

An Unusual Alcohol Slide Rule

Introduction

In the latter half of the eighteenth century the standard slide rule used for assessing the duty on wines and spirits was the Everard type with a nearly square cross-section and a single slide on each face (four slides in total). These are well known and have been described in many papers including my previous one 1, “The Missing Link”. Towards the end of the eighteenth century a simpler form of gauger’s slide rule appeared having just two slides located on the upper face of a rectangular section rule. These have been described previously by Thomas Wyman 2 and Mark and Jane Rees 3. All of the rules described in these references have been simpler, with plain backs and no variety lines

The Unusual Rule

From time-to-time people email me, using the contact details on my website, offering to sell me an item for my collection and occasionally it is something of interest, a price is agreed, and the item duly arrives. This is one such item. I had always wanted to add a slide rule of this configuration to my collection but, until it arrived, I had no idea that it would turn out to be a previously (as far as I know) unrecorded type. It is illustrated in figures 1 and 2.

Figure 1

Figure 2

Unfortunately it is rather worn and does not photograph well so I will describe each of the scales in turn, from top to bottom in each case. The first scale is in fact two scales, one on the left hand side and one on the right; the left hand one runs from 1 to 3.2 and is effectively the first half of a single radius logarithmic scale. It has two gauge points with brass pins for the pre-1824 wine and ale gallons. The right hand half is a logarithmic scale from 1-10 (actually equivalent to one half of a double radius 1-10/1-10 scale); it has two gauge points, one for the malt bushel, marked MB, and one for the number of cubic inches in an ale gallon, marked A. The scale on the upper slide is a double radius logarithmic one, 1-10/1-10.

The next scales are on the upper half of the central strip and these are more unusual ones, at least on this type of rule. There are actually two scales, each occupying half of the length. The first (on the left hand part) is a single radius logarithmic scale folded at about 3.2. On it there are two gauge points, MS and MR, respectively for the side of a square vessel containing one malt bushel per one inch depth and for diameter of a cylindrical vessel containing one malt bushel per one inch depth. It is effectively a continuation of the left hand scale at the top of the rule, previously described. This is in fact the normal arrangement on one of the sides of a four slide Everard type rule.

The second scale, on the right hand half, is a reciprocal scale folded at 2150, the number of cubic inches in a Winchester malt bushel. It is the malt depth scale and labelled MD. Below these scales is a double radius scale marked 1-10-100. It is marked SS for segment standing. The slide is again double radius logarithmic marked 1-10/1-10. The final scale is a segment lying scale commencing about 1/3 of the length from the left hand edge, again marked 1-10-100.

The reverse of the rule has the variety scales for spherical, second and third varieties and the associated inch scale representing the difference between the head and bung diameters of the cask. The rule measures 12 x 1.6 x 0.4 inches.

Conclusion

This rule differs from other single sided, dual slide, slide rules previously described. On the one face it in fact has all the usual scales found on a four slide Everard type rule. Clearly these are compressed compared to a twelve inch Everard type rule so the resolution and accuracy are reduced in proportion. The presence of the variety scales on the reverse means this rule can carry out all the functions required by a gauger.

Acknowledgements

I am very grateful for the help provided by P A (Tom) Martin in identifying the functions of various parts of this unusual slide rule.

1. David M Riches, The Missing Link, Bulletin of the Scientific Instrument Society No.115, December 2012 and the Slide Rule Gazette Issue 14, Autumn 2013. The slide rule illustrated here is a post 1824 one with Imperial gauge marks but the construction of the pre-Imperial ones was the same and one can be seen on http://www.mathsinstruments.me.uk/page11.html

2. Thomas Wyman, SOHO Steam Engines, The First Engineering Slide Rule and the Evolution of Excise Rules, Proceedings of the 18th International Meeting of Slide Rule Collectors, pp 63-72. He lists and describes seven single sided, two slide, slide rules. All have plain backs and a simplified set of scales.

3. Jane Rees and Mark Rees, The Rule Book - Measuring for the Trades, Astragal Press, 2010, ISBN 13: 978-1-931626-26-2, page 221. It also notes that these rules were invariably longer (18 or 24 inches).