Herman Hollerith: Electric Tabulating Device, 1890
Mercury CupsThe mechanical/electrical detection device for each column consisted of a hard rubber bedplate containing an arrangement of small cups of mercury which coincided with each possible hole location on the card. After placing the card over this array the operator pulled down a "pin-box" of spring-loaded pins with exactly the same arrangement as the mercury cups. Pins which passed through a hole dipped into the mercury cups and completed the circuit to an electromagnet which advanced the corresponding counter dial by one unit. The operator hand copied the tabulation totals and reset the dials to zero at the end of each run.
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