A pocket slide rule. Photo acquired from Wikimedia Commons, the free media repository

The first time I entered the math library at Lebanon Valley College, I was struck by what I saw on top of the bookcases – a giant slide rule! Though I had never used one, I remembered my dad telling me about how he had to use a slide rule in his math classes in college. This iconic piece of mathematical technology owes its existence to the mathematical development that is celebrating its 400th birthday this year – the invention of logarithms.

I recently came across a link to a Science News article by Tom Siegfried entitled Logarithms celebrate their 400th birthday. The article discusses how John Napier revolutionized mathematics in 1614 with his invention of logarithms. Though many considered the logarithm a godsend, not everyone was convinced.

Napier’s mathematical wizardry wasn’t universally appreciated, though, as rumors swirled that he was actually a dark wizard, à la Lord Voldemort. For one thing, Napier’s grass seemed to be greener than other landowners. And he allegedly trained a magical black rooster to identify thieves among his workers.

The article also discusses how the invention of logarithms led to the development of the slide rule.

It wasn’t long until others figured out how to put the logarithms to use in mechanical calculations using sticks. Inscribing numbers on the sticks at intervals proportional to their logarithms made it possible to multiply numbers by proper positioning of the sticks. Edmund Gunter, a London clergyman and friend of Briggs, had the germ of the idea in 1620. But the honor of first to slide the sticks is usually accorded to William Oughtred, an Episcopal minister, who also devised a circular version of the slide rule in the 1620s.

The invention of logarithms introduced a new way for quickly performing complicated calculations, with one mathematician claiming that “logarithms effectively doubled a mathematician’s useful lifetime.” Without the tools that logarithms offer the sciences today, our understanding of the world would be greatly limited.

## About Stephanie Blanda

Stephanie is a math Ph.D. student, with a minor in Computational Science, at Penn State University. She obtained a B.S. from Lebanon Valley College, where she double majored in Mathematics and Computer Science. Currently, Stephanie is studying the interface of two viscous fluids under a shear flow, specifically with applications to wind generated ocean waves.

I enjoyed learning how to use a slide rule (in high school). It provided a very tactile way of doing computations. Also, the slide rule did the hard part of the work for you, but the user had to think about what the computation really was so that it could be done on the slide rule. Thus, the user was more deeply engaged, which led (for me, at least) to a better understanding of computation.

As a present, my parents bought me a giant slide rule that came from my old high school. It was the demonstration slide rule that hung on the front wall of a math classroom. Unopened it was about 8 feet long. I had it in the hallway in my apartment in grad school. When I graduated, I couldn’t take it with me immediately, since I was shipping everything via UPS. (The slide rule exceeded their length + girth restriction.) Since more math grad students were moving in, I left it behind, with the plan to pick it up at the end of the next year. Alas, when I came back, the roommates had cycled through to a new group and the slide rule was gone.