From Blaise Pascal to Charles Babbage many people have tried to build calculating machines. Babbage wished "to calculate with steam" and use the power of the newly developed steam engine to drive first his Difference Engine and then his Analytical Engine. Mechanical calculating devices have been available even until the early 1970s, but it was Herman Hollerith who added electricity to the process of calculating in 1890.
During the U.S. census of 1890 the United States government was faced with an enormous mass of calculations. Rather than hire more clerks and bookkeepers, the Census Bureau went looking for a solution. While Hollerith's Tabulating Machine was not a computing device like the ones designed by Babbage, it did two important things: it performed simple calculations like addition and it did it with a combination of mechanical parts and electricity. The mechanical parts moved the punched cards through the Tabulating Machine but it was a series of electrical parts that performed the actual "reading" of the card.
After Hollerith established the Tabulating Machine Company many other companies continued to make mechanical calculating devices, but an ever increasing use of electricity mean that the future of computing would be electronic.
Timeline for Elecro-Mechanical Computing
The names on this timeline represent a few of the people who made important contributions to the development of electronic computers.
In 1906 Lee De Forest developed the "Audion tube", which was a three-element vacuum tube that played a key role in the development of the radio. This Audion tube would later be used as a core component in electronic computers.
Some histories credit John Ambrose Fleming with inventing the Vacuum tube. This is not entirely wrong. In 1904 Fleming invented and quickly patented (a lesson he learned while working with Thomas Edison) a two-element vacuum tube or diode. He called it a Fleming Valve.