What are the Jaquet-Droz automata, and why are they called early computers?

Picture a child-sized doll sitting at a little desk. It dips a goose-feather pen into an inkwell, shakes off the extra ink with a flick of the wrist, and begins to write a sentence in neat letters, its eyes following the pen across the page. No one is touching it. The doll is about 250 years old, and it still works.

That doll is the Writer, the most complex of three automata made in Switzerland in the late 1700s. (The family name is spelled Jaquet-Droz; you will sometimes see it written Jacquet-Droz.) What makes the Writer special is not only its skill but the fact that you can change what it writes. You set the text, and the machine carries it out. That is the basic idea of programming.

Who made them, when and where

The three automata were built between 1768 and 1774 in La Chaux-de-Fonds, a watchmaking town in Switzerland. Their makers were:

• Pierre Jaquet-Droz (1721–1790), a watchmaker who ran the family business;
• Henri-Louis Jaquet-Droz (1752–1791), his son;
• Jean-Frédéric Leschot (1746–1824), who worked with them.

The six-year span covers the three dolls together; an exact completion date for each one is less certain. The dolls were not made for science. They were showpieces, built to draw attention and help the firm sell watches and mechanical birds to wealthy customers across Europe. They toured widely and changed hands several times. In 1906 the History and Archaeology Society of Neuchâtel bought them for 75,000 gold francs, and on 1 May 1909 they were given to the City of Neuchâtel. They have been a highlight of its Museum of Art and History ever since, and museum staff still run them for visitors.

The three dolls

The Musician is a young woman seated at a small organ built for her. She really plays it, pressing the keys with her fingers; the music does not come from a hidden music box. Her chest rises and falls as if she were breathing, and her head and eyes follow her hands. She contains about 2,500 parts.

The Draughtsman is a small boy who can produce four different pictures, including a portrait of King Louis XV and a dog with the words "Mon toutou" ("my doggy") beside it. Now and then he blows on his pencil to clear away dust. He has about 2,000 parts.

The Writer is about 70 centimetres tall and has roughly 6,000 parts. He can write any custom text up to 40 characters long.

How the Writer works

The key part inside these dolls is the cam. A cam is a flat disc with a carefully shaped edge. As it turns, a small lever resting on the edge rides up and down, following the bumps and dips. Link that lever to a doll's arm, and the shape of the disc becomes a movement of the hand. In other words, the cam stores a motion in metal.

To draw or write, the hand has to move in three ways: left and right, up and down the page, and lifting the pen on and off the paper. The Draughtsman uses sets of cams that encode those three movements for each picture.

The Writer adds a crucial layer. It has a set of cam groups, one group for each letter it can form. In front of them sits a wheel on which the operator selects characters one by one, up to 40. As the machine runs, the wheel steps from one setting to the next, and each setting tells the mechanism which letter's cams to follow.

Here is the idea as a worked example. Suppose you want the Writer to write "BON":

The letter shapes never change; they are fixed in the cams, much like the permanent memory in a computer. The wheel is what you change, much like a program or a document you type. Separating what the machine knows how to do from the instructions you give it is exactly the design behind every computer you use.

Why it mattered

The Jaquet-Droz dolls fascinated royal courts in their day, and they still draw crowds in Neuchâtel. For historians of technology they matter because they show, in brass and steel, that a machine could be built to perform a complex task and be reprogrammed for a different one without rebuilding it. They predate Charles Babbage's designs for calculating engines by decades.

It is worth being clear about what they are not. The dolls sense nothing and decide nothing. The Writer has no way to notice if its paper slips or its ink runs dry. Every movement was worked out in advance by their makers. In 2019 that is still how most factory robots work: they repeat a programmed path with great precision. The newer robots in research labs, which learn from cameras and practice, are trying to do the part the Writer never could.

What is the difference between a programmed machine and an intelligent one?

A programmed machine does exactly what its instructions say. The Writer will form any 40 characters you set, but it cannot notice a spelling mistake, choose a better word or adapt when something goes wrong. All of the cleverness lives in the people who designed the cams and the person who set the wheel.

An intelligent system, in the sense AI researchers use the term, has to handle situations its designers did not spell out one by one. It needs some way to take in information about the world, such as a camera or text, and some way to choose what to do with it. Modern systems often learn those choices from examples rather than following hand-written steps.

The line between the two is not always sharp. Every AI program is still, at bottom, a program running on a machine. The difference is how much of the behavior was written out in advance, and how much the system works out for itself. The Writer sits at one end of that scale, beautifully and completely programmed.