Grades 3–5 · History & Evidence
How could holes in cards tell a loom which threads to lift?
A patterned woven fabric depends on which lengthwise threads rise before a crossing thread passes through. A Jacquard mechanism used punched cards to help control those choices. The cards stored instructions as a pattern of holes and solid places.
In the diagramCard choices select threads before weavingholes / solid placeshooks select thread heightscrosswise thread passes throughCard choices become a pattern through repeated weaving.
When a card met the reading mechanism, a hole let a matching part move differently from a solid area. This selected which hooks could lift their connected threads. Many thread choices could be controlled during one step.
The loom then passed a crosswise thread through the opening between raised and lowered threads. Advancing to another card changed the next selection. A chain of cards could therefore describe a pattern across many rows of cloth.
The cards did not contain a tiny picture that was stamped onto the cloth. They controlled repeated mechanical actions that built the picture through weaving. This made a stored sequence useful for producing complex patterns more than once.
About this explanation
Starting knowledge: Know that cloth has crossing threads and that a sequence of marks can carry instructions.
Sources
- Science and Industry Museum — Weaving numbers: The Jacquard loom and early computing