(3/4) Exploring how the differential analyser works in simple terms

University of Kent historian Tom Ritchie discusses and demonstrates the unlikely link between the children’s toy Meccano and the birth of computers as part of his History Ph.D. project (in collaboration with the Science Museum, Kensington).
Tom, working with two 'Meccanomen' (Ian Henwood and Matthew Goodman), explores how the rebuilt differential analyser works.
This demonstration was designed to appeal beyond simply those who traditionally attend academic lectures, engaging children, young adults, and the general public, avoiding jargon and confusing language as much as possible, to help them engage with challenging historical, mathematical and engineering concepts in a simple, 'hands-on' way.
This was organised with the help of the Templeman Library, the Special Collections and Archives Team, the School of History, the Science Museum.
For more on this project and other work:
Personal Blog: tomritchie.co.uk/
Twitter: @Tom_Ritchie1
Email: [e-mail]
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When asked to think about computers, what is the first thing that comes to your mind - maybe the big ones, like Steve Jobs and the iPhone, Bill Gates and the Microsoft computer, or Alan Turing and Enigma?
But very few of us would think of Douglas Hartree and his Differential Analyser. Yet, before the Second World War, in 1934, Hartree and this analogue computer were at the forefront of computing, both in Britain and abroad. In fact, the Hartree Differential Analyser was the first analogue computer of its kind to be built in the U.K.
What are analogue computers? Analogue computers rely on the mechanical movement of continuously changing physical quantities to create answers. Whereas digital computers - the laptops and smartphones that shape our world today - resolve equations, using binary language (i.e., in the form of 0 and 1).
Put simply, if you could look at analogue computers in action, you would actually be able to see an equation move through them mechanically, from the input table, through the integrating units, to the answers that are drawn by the output table.
This was the genius behind Douglas Hartree’s alternative approach to computing. His analyser was only the beginning. It led to the development of a number of other machines, which were used during the Second World War to calculate anti-aircraft ballistics trajectories and the Tube Alloys initiative (Britain’s own nuclear weapons programme).
What makes the Hartree Differential Analyser even more impressive is the unlikely material it was built with. Forget diodes and motherboards, Douglas Hartree and his research student Arthur Porter constructed one of the world’s first computers from the children’s toy Meccano.

[@goodmaro]

You're spending so much time on minor details like scaling factors, yet this far in to the explanation I still don't see how this thing can do differentiation. Integration on a time or other arbitrary independent variable I see it doing easily, just keeping a running sum of how far a wheel turns. But I don't see anything allowing you to do it the other way, giving an output of the rate of an independent variable on another.