Percy Ludgate

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Percy Edwin Ludgate (August 2, 1883 – October 16, 1922) was an accountant in Dublin and designer of an Analytical Engine.

Percy Ludgate was born in Skibbereen Co. Cork and studied at Rathmines College of Commerce, where he was a gold medal student, before joining a Dublin firm of accountants. From 1903 he spent his spare time designing his analytical machine. Possibly this first portable computer — more “table top” than “laptop” — was designed around 1907, although it was never built. He presented the details to the Royal Dublin Society in 1909. This brought him to international attention, and in 1914 the Royal Society invited him to lecture in Edinburgh at a special conference on mathematics and computing.

Since the invention of the abacus, people have been trying to build more complex calculating machines. Charles Babbage (1791-1871), the ‘grandfather of computing’, spent years and a fortune designing his programmable calculating machines. His ideas were based on the Jacquard loom, where punched cards controlled the patterns. But his machines were impossible to build; only small sections were ever attempted. And even these were enormous, ponderously slow – everything was reduced to addition or subtraction – and required thousands of precision-engineered metal parts.

Ludgate’s design was also based on the Jacquard loom, but was different in most other respects from Babbage’s machine, and when Ludgate started on his ideas, he knew nothing of Babbage. Where Babbage used columns of toothed discs to store numbers, Ludgate opted for a simpler, more-loom-like shuttle mechanism.

Ludgate’s analytical machine was programmable, yet small enough to be portable, and it had all the elements of a modern computer: a) a mechanism for storing data, b) ways to input data and program the machine (using pre-punched ‘formula’ tape and/or keyboards), c) an ‘operating system’ of sorts, and even d) a printer, all of which Ludgate designed himself. (More details: article from The Computer Journal, 1971)

Ludgate’s machine had two especially innovative features: it could be stopped at any stage in a calculation to add new variables, and it could do subroutines. (Ludgate’s approach to calculations was also unusual: for multiplication he developed a technique using partial products; for division he used a table of reciprocals and a rapidly converging series using subroutines.) His method of implementing multiplication was referred to at the time as "Irish logarithms". (Boys, 1904)

He calculated that his engine would multiply two 20-digit numbers in under ten seconds and take two minutes to determine the logarithm of a number. It could also be set to solve algebraic equations and geometric problems. Ludgate envisaged it would be powered by an electrical motor, and the calculations automated. The complete device, measuring about two feet in every direction, would be portable.

Unaware at the time of Babbage's designs, he later went on to write about Babbage's machine. Ludgate's design used multiplication as its base mechanism in contrast to Babbage's, which used addition, It also called for rods similar to slide rules. Its precise mechanism is unknown as the only written accounts of the engine which survive do not detail its workings.

Ludgate also helped advance calculators by expanding Babbage's design for the first programmable computer. He was one of a few independent workers in the field of science and mathematics. His inventions were worked on outside a lab, and then only part-time.

During World War I Ludgate was diverted to work on a committee organising the supply of oats for the British cavalry, and he seems not to have returned to his computer.

Little is known about Ludgate's life, as his only records are his scientific writings. The best source of information about Ludgate and his significance lie in the work of Professor Brian Randell.

Ludgate died of pneumonia aged 39, after returning from a Swiss walking holiday. In 1991 the British Museum constructed the first complete Babbage difference engine. Sadly, little of Percy Ludgate’s design survives, so we will probably never see a working model of this pioneering Irish calculating engine.

In 1991, a prize for the best final year project in the Moderatorship in computer science course at Trinity College Dublin – the Ludgate Prize – was instituted in his honor.

In 2015, a group of established business people set up a non-profit company in the name of Ludgate in Skibbereen, Co. Cork, with the aim of developing the local economy through the medium of digital technology and local innovation.



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