Electricity - Schematic Diagrams I - Teacher's Notes
schema
A Greek word, meaning plan or diagram. The original schema were drawings of the heavens, showing the position and relationships of the stars.

diagramma
A Latin word, meaning a line drawing used to explain a concept or plan.

Showing Connections
 Our notation for representing wires that cross without connecting has changed within the last 50 years. In earlier times, two wires that did not connect would be shown as "not touching", like the top figure to the left. Later, some draftsmen would show "not touching" like the lower figure to the left.   Likewise, our notation for representing wires that connect has also changed. In earlier times, it was only legal to show a connection with three wires, and the dot at the connection was not required (see the top right). A connection of four wires at the same point was not legal, and so draftsmen would use the notation shown at the lower right when they needed to show four wires connecting.