Work relations

Photograph of Thomas Edison by Victor Daireaux, Paris, circa 1880s

Frank J. Sprague, a competent mathematician and former naval officer, was recruited by Edward H. Johnson and joined the Edison organization in 1883. One of Sprague's significant contributions to the Edison Laboratory at Menlo Park was to expand Edison's mathematical methods. Despite the common belief that Edison did not use mathematics, analysis of his notebooks reveal that he was an astute user of mathematical analysis conducted by his assistants such as Francis Upton, for example, determining the critical parameters of his electric lighting system including lamp resistance by a sophisticated analysis of Ohm's Law, Joule's Law and economics.^[44]
Another of Edison's assistants was Nikola Tesla. Tesla claimed that Edison promised him $50,000 if he succeeded in making improvements to his DC generation plants. Several months later, when Tesla had finished the work and asked to be paid, he said that Edison replied, "When you become a full-fledged American you will appreciate an American joke."^[45] Tesla immediately resigned. With Tesla's salary of $18 per week, the payment would have amounted to over 53 years' pay and the amount was equal to the initial capital of the company. Tesla resigned when he was refused a raise to $25 per week.^[46] Although Tesla accepted an Edison Medal later in life, this and other negative series of events concerning Edison remained with Tesla. The day after Edison died, the New York Times contained extensive coverage of Edison's life, with the only negative opinion coming from Tesla who was quoted as saying:

"He had no hobby, cared for no sort of amusement of any kind and lived in utter disregard of the most elementary rules of hygiene. [...] His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90% of the labour. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense."

—Nikola Tesla

It seems very likely that Tesla's description was accurate, considering one of Edison's famous quotes regarding his attempts to make the light globe:

"If I find 10,000 ways something won't work, I haven't failed. I am not discouraged, because every wrong attempt discarded is another step forward".^[47]

—Thomas Edison

When Edison was a very old man and close to death, he said, in looking back, that the biggest mistake he had made was that he never respected Tesla or his work.^[48]
There were 28 men recognized as Edison Pioneers.