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John W. Mauchly and the Development of the ENIAC Computer

Early Experiments

Ultimately, it was the difficulty Mauchly experienced in getting his colleagues to accept his meteorological studies that prompted him to explore digital, electronic methods of computation. Established meteorologists were highly skeptical of the statistical approaches to the study of their field. Mauchly had worked for two summers at the Department of Terrestrial Magnetism of the Carnegie Institute of Washington, D.C., studying data on diurnal variations in the ion densities of the ionosphere. His paper on the subject, however, had been rejected, especially for its use of "so short a period" of analysis. Because Mauchly had followed these variations for only a month, reviewers considered his conclusions unwarranted. And yet the information they wanted required more extensive data analysis than Mauchly could easily perform with the resources at his disposal.
J. W. Mauchly, chart of radio transmission disturbance over North Atlantic, 1937-38, from article, "Depression of Mid-day Ion Densities in the F(sub-2)-region of the Ionosphere related to the Diurnal Variation of H.," for Union Radio Scientique Internaionale, 1938. (click to expand to 83k)
This fact prompted Mauchly to begin some early experiments with digital electronic computing circuitry. His two years as an undergraduate in an electrical engineering department no doubt fueled this new twist in his research. His resources were small, as was the scale of these trials. Among the circuits that he built were such basic elements such as a "flip-flop," which could essentially store the "1s" and "0s" that make up the information stored by all digital computers.* Mauchly built some of the circuits using neon bulbs rather than the more expensive vacuum tubes, which meant that they did not have the full performance of vacuum tube circuitry. Nor was he the first to discover these devices. Electronic counters and other devices had been developed earlier.* Nevertheless, Mauchly was beginning to figure out the basic concepts behind electronic computing circuitry himself.

Letter from Knox McIlwain to J. W. Mauchly, 14 May 1941. (click to expand to 138k)
This new interest eventually led Mauchly to the University of Pennsylvania. He received a letter from Knox McIlwain, the Director of Engineering Defense Training at the university's Moore School of Electrical Engineering. The Moore School stood at the heart of a strong regional electrical industry that had grown with the popularity of radio, telephony, and other electronic technologies. With the prospects of war looming, the military began to seek young engineers trained to operate the electronic weapons and communications systems that were becoming an increasing part of U.S. armaments. The Moore School stepped forward to accept a contract from the U.S. Army to teach a special ten-week course on Electrical Engineering for Defense Industries directed to students with a degree in mathematics or physics. McIlwain had written Mauchly as the Chair of Ursinus' Physics Department, inquiring whether he knew of prospective students. But Mauchly wanted to learn more about electronics himself, not the least because of his interest in computing circuitry.

The outcome was that in 1941 Mauchly himself enrolled in this program, even though he already held a Ph.D. in physics.

Cover of brochure for "Training in Electrical Engineering for Defense Industries" courses at Moore School, University of Pennsylvania, 1941. (click to expand to 110k)

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