Abstract

In 1876 Professor Sir William Thomson, who later became Lord Kelvin, published a series of papers that are seen as the basis for subsequent developments in analogue simulation and for many of today’s simulation software tools. Sir William proposed that a type of mechanical integrating device designed by his brother, Professor James Thomson, could be used directly to solve ordinary differential equations of any order. Although not implemented in the nineteenth century, the ideas resurfaced in the 1920s and 1930s in the work of a team at the Massachusetts Institute of Technology (MIT) under the direction of Vannevar Bush. At that time there was much interest in the possible use of mechanical methods for system analysis and design in the field of electrical power systems. This led to the development of “integraph” devices and to the mechanical differential analysers for which Bush is rightly famous. As we approach the 150th anniversary of the publication of the key papers by Sir William Thomson and his brother in 1876 and also the centenary of the developments at MIT in the mid-1920s, it is appropriate to review the significance of these early developments which represent important historical milestones in simulation methods. Many of the ideas and principles established by Kelvin and Bush remain valid today but their origins are seldom fully recognised.