This list is very much a "work in progress" as names or facts come to light...
People
Oliver Heaviside...British physicist and mathematician whose theoretical work played a large part
in the understanding of radio transmissions and long distance telephony.
First published work (July 5, 1872, p. 411.) under the signature "O" titled "Comparing electromotive forces".
William Matthew Flinders Petrie known as a pioneer in the field of archaeology and Egyptology,
at the age of 17 he writes under his initials W.M.F.P a letter on the Great Pyramid,
(Dec 16, 1870, p. 303)
"Jack of all Trades"...the pen-name of the most prolific correspondent to the pages of EM, from 1871 to 1919
he wrote an estimated 9,000 replies and queries to the paper, his real name was John Joseph Haselgrove.
(Photograph & short biography from his son)
Facts
The Motor-car, on (April 3rd, 1896, p135) some months before the Act of Parliament
allowing vechicles to run on the roads, the first real working instructions on
building a motor vehicle given in any journal were given by Mr. F. C. Blake.