The history of the scientific slide rule, that important tool of almost all scientists and engineers until the early 1970s, goes back to the early 1600s when Scottish mathematician John Napier first published a document on logarithms (logs).Various crude devices that allowed one to mechanically add and subtract logs (equivalent to multiplication and division) with movable sections (sliding rulers) were then devised over the next two centuries, but it was not until 1859 that the basis for the modern slide rule was established in Germany by Victor Mannheim. Mannheim’s early slide rules were often made of mahogany but by 1887 the factory of A.H. Faber (later Faber-Castell) used a celluloid facing on the wood for the markings. About that time significant advances were made in the precision of engraving of plastics and several additional companies began the production of slide rules. New companies emerged on the scene around 1900. One was Hughes-Owens, who used a system developed by Hemmi in Japan for accurately engraving a celluloid coating on a bamboo base. Another was the famous instrument company, Keuffel&Esser (K&E). Both “student” (10-inch) and higher precision 20-inch versions became readily available on the market. Some versions of slide rules developed after 1900 were capable of being used for many more mathematical and engineering functions. Whereas the earliest versions had only a few scales engraved (typically 7-9), later versions had up to 21 scales in double-sided versions. Typical accuracies that could be achieved with these devices were 0.1%, however, the user had to mentally keep track of the position of the decimal point. The Canadian Nuclear Heritage Museum (CNHM) has a collection of slide-rules manufacture by all three of the above-named companies and both 10-inch and the 20-inch versions. Our most recent donation is also the oldest. It was donated recently by John Hilborn, who inherited it from his father. It is a 20-inch, celluloid-on-mahogany, K&E 4053-5 model that research on the internet reveals was manufactured between 1909 (when the 4053 series first appeared) and 1913 (when the inches ruling along the side was switched to centimeters).The death knell for the slide rule came in 1972 when the Hewlett-Packard HP-35 scientific pocket calculator made its appearance. The 35 key unit (hence model 35), which sold initially for $395(US), quickly became a “must-have” for all scientists and engineers. Many of us who worked at Chalk River at that time quickly acquired one of the calculators, or at least attempted to. The calculators normally were installed with a locked cradle and a four-foot-long steel cable that was very securely looped through a newly drilled hole in the top of the two-inch thick Chalk River wooden desks of the day. (Equivalent-quality versions of the HP-35 calculator are today available for $30 or less.)
Visitors to the CNHM are welcome to try their hand at using the various slide rules to solve some mathematical/engineering problems. We are fortunate to have two manuals which were also donated and can be used for guidance. To arrange a visit, send a message to info@nuclearheritage.com
