Logic Machines

Logic Machines

As we may or may not have previously discused (depending on the way in which you're bouncing around our web pages), these days we are predominantly concerned with computers, but it's worth noting that there has historically been a great deal of fascination in logic in general. This fascination was initially expressed in the form of logic diagrams, and later in the construction of special-purpose logic machines for manipulating logical expressions and representations.

The world's first real logic machine, in the sense that it could actually be used to solve formal logic problems (as opposed to those described in Ramon Lull's Ars Magna, which tended to create more problems than they solved), was invented in the early 1800s by the British scientist and statesman Charles Stanhope (third Earl of Stanhope). A man of many talents, the Earl designed a device called the Stanhope Demonstrator, which was a small box with a window in the top, along with two different colored slides that the user pushed into slots in the sides.		Although Stanhope's brainchild doesn't sound like much it was a start (and there was more to it than we've covered here), but Stanhope wouldn't publish any details and instructed his friends not to say anything about what he was doing. In fact it wasn't until around sixty years after his death that the Earl's notes and one of his devices fell into the hands of the Reverend Robert Harley, who subsequently published an article on the Stanhope Demonstrator in 1879.
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Working on a somewhat different approach was the British logician and economist William Stanley Jevons, who, in 1869, produced the earliest model of his famous Jevons' Logic Machine.
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The Jevons' Logic Machine was notable because it was the first machine that could solve a logical problem faster than that problem could be solved without using the machine! Jevons was an aficionado of Boolean logic, and his solution was something of a cross between a logical abacus and a piano (in fact it was sometimes referred to as a "Logic Piano"). This device, which was about 3 feet tall, consisted of keys, levers, and pulleys, along with letters that could be either visible or hidden. When the operator pressed keys representing logical operations, the appropriate letters appeared to reveal the result.		The next real advance in logic machines was made by Allan Marquand, whom we previously met in connection with his work on logic diagrams. In 1881, by means of the ingenious use of rods, levers, and springs, Marquand extended Jevons' work to produce the Marquand Logic Machine. Like Jevons' device, Marquand's machine could only handle four variables, but it was smaller and significantly more intuitive to use. (Following the invention of his logic machine, Marquand abandoned logical pursuits to become a professor of art and archeology at Princeton University.)
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Things continued to develop apace. In 1936, the American psychologist Benjamin Burack from Chicago constructed what was probably the world's first electrical logic machine. Burack's device used light bulbs to display the logical relationships between a collection of switches, but for some reason he didn't publish anything about his work until 1949.
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In fact the connection between Boolean algebra and circuits based on switches had been recognized as early as 1886 by an educator called Charles Pierce, but nothing substantial happened in this area until Claude E. Shannon published his 1938 paper (as is discussed elsewhere in this history).		Following Shannon's paper, a substantial amount of attention was focused on developing electronic logic machines. Unfortunately, interest in special-purpose logic machines waned in the 1940s with the advent of general-purpose computers, which proved to be much more powerful and for which programs could be written to handle formal logic.

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These notes are abstracted from the book Bebop BYTES Back (An Unconventional Guide to Computers) Copyright Information