Antique Dring & Fage Wooden Slide Ruler With Bone Middle Insert. Over the 19th and much of the 20th Centuries the slide rule was the primary instrument for calculation used in trading and engineering. Although originally invented in the 17th Century, and widely used for gauging (or estimating the quantities of certain products, such as alcoholic spirits), it took until around 1850 for the slide rule to become generally popular. 

Size: 12 1/4 x 1 1/2 x 1/8 in. 

#2942 #14 . 

In 1784 instrument and glassmaker John Dring opened a company in Walworth, a district of South London. Over the next six years he developed as a brassmaker as well, particularly while creating items for a businessman named William Fage. In 1790 Dring took over another business founded by John Clarke, the father of his son-in-law, and brought Fage on to handle the load. They created Dring & Fage, becoming the primary manufacturers of hydrometers and mathematical instruments in the capital, as well as the saccharometer, which Clarke had invented. These instruments were primarily used for excise purposes, especially measuring the strength of alcohol. The company moved locations several times, with 11 different addresses over their entire history. By 1850 the company, still operating under the same name, was owned by Edward Hall and Edward Jenkin, who were appointed Hydrometer and Saccharometer Makers to the Board of Inland Revenue. The business then passed to Hall’s daughter Julia and her husband Alfred Jones in the late 19th Century, and from them to Edward Jones. In 1940 the company became Dring & Fage Ltd, and continued to trade at least into the 1960s, although it is unclear exactly when the company finally went out of business.