The Jacquard Loom

Until a couple of decades ago, computer programs were generally punched onto 80-byte cards, the cards dating back to Herman Hollerith, who introduced a machine in the late nineteenth century to process the information resulting from a population census of the United States.

The basic idea of coded cards came earlier. Nowadays, placards displayed in the windows of haberdashery shops may advertise multicolored beach towels or the like as having a "Jacquard weave." That is, the pattern is not merely printed onto the material; rather it is woven into the fabric. It was a Frenchman, JosephMarie Jacquard (1752—1834), who invented the first loom capable of producing such designs.

But how did the Jacquard loom manipulate the weave? That is, how did it instruct which longitudinal threads to move upwards, and which down, as the bobbin carrying the cross-thread in the weave shuttled from side to side? The answer is that the instructions were carried by a series of holes cut into flat tablets of wood, a hole in a specific position causing a particular thread to be raised, whereas unpunctured wood had the effect of making the thread drop.

An equivalent system is the punched-hole stack of connected cards used in a pianola, or the rotating slotted-metal disk in a nickelodeon, where the music is being played in response to the arrangement of the holes. Similar principles are at work in many fairground organs and the like.

There is a specific link to the development of computers here. If Charles Babbage had ever managed to complete the "analytical engine" that he began in the 1830s, it would have been the first programmable computer, although a mechanical rather than electronic device. Babbage, an Englishman, disparaged his own country greatly, but was a great admirer of what he saw as the superior ingenuity of other Europeans. He knew all about Jacquard looms. Babbage's intention was to read both data and program instructions into his machine using a card system copied from the Jacquard concept.

This is connected with eclipses in two ways. The first is that Babbage's specific initial motivation was the automated computation of mathematical and astronomical tables, such as might be used to predict eclipses. His initial fledgling device, begun a decade or so earlier, which again was never completed, was the "difference engine," a straightforward calculating machine rather than a programmable computer. Its development was funded in part by the British government on the grounds that the nautical almanac used for navigational purposes by the Royal Navy and merchant shipping was rife with anomalies. These were due to mistakes made in the complicated calculations performed longhand by human computers, rather than the error-free machines that Babbage claimed he would be able to construct.

The second point connecting to eclipses is that a Jacquard weave provides an excellent parallel to the patterns of eclipse occurrence.

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