Re: Humanity!

Alan Williams

I agree with the sentiment that "Sometimes you find a special slide rule and after studying its use and construction you discover that the person behind the object is much more interesting than the slide rule itself". This is exactly what happened in the last few days after my post about the Davis-Pletts rule, having been prompted to look into the life of its originator, John St. Vincent Pletts. I'm sure his short but eventful 44-year life would make a gripping read.

A similar episode occurred a few years ago when I was just starting my collection and purchased a couple of special-purpose slide rules for calculating the perforation of Firth-Brown's armour plate by "Tresidder's formula", having long been interested in Sheffield's steel industry. On receiving them I noticed that, although basically pristine, both rules were covered in faint pencil notes and numbers which I considered gently removing with a soft eraser, but for some reason never got around to doing.

A few weeks later, I noticed that the same seller had auctioned several other unusual devices including a complicated-looking angle measuring tool with a patent marking. This also turned out to be the invention of a Captain Tresidder, so I contacted the seller to find out where the items had originated. It turned out that they all came from the effects of Captain Tolmie John Tresidder, another fascinating figure with a long and illustrious career in the steel industry. The development of naval armour and the projectiles designed to penetrate it were almost the space race of the early 20th century, culminating in the First World War. The slide rules had been Tresidder's own working examples that he annotated with additional figures and notes, having originally accompanied a manuscript of a speech that he had given on the subject of armour plate (which unfortunately I was unable to reunite with the rules).

Suffice to say I have never been so pleased not to have cleaned a slide rule, an ethos I continue to live by.

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