I should also point out that Loomis' work did not involve radio waves at all. He was correct in identifying disruption of existing electrical currents in the atmosphere as being the 'modus operandi' of his system. He was only wrong in thinking there was a charged layer close enough to the ground that it could be tapped into for useful amounts of power. Like the thermal-energy microwave communication idea, it is a clever application of known physical principles, but will never become useful for very many practical purposes...because in physics, as every other endeavor, there is no such thing as a free lunch.Some later apologists like to speculate that Loomis' key closures and openings constituted a rudimentary spark gap transmitter. Sure, a little momentary radio noise would have been generated in the process, but that would not have been detected by a plain DC galvanometer of that day. I believe AC galvanometers were under development at the time, but they were (a) bulkier, (b) less sensitive (crucial, because the spark at the sending end typically would have been the result of less current flow than connecting a #47 pilot lamp to a battery), (c) too slow to respond to a momentary damped-wave emission at the instant of connection or disconnection (the only time waves would be produced, not during key-down), since both a stationary and moving coil are required with AC versions; and (d) were expensive laboratory curiosities for many years.
Loomis was neither the only nor the first experimenter in non-radio wireless telegraphy. The best overall reference on the subject is probably John Joseph Fahie's A history of wireless telegraphy, 1838-1899 : including some bare-wire proposals for subaqueous telegraphs. It is available in public-domain reprints through Amazon.com and can sometimes be found in readable form online.
It is the second of three volumes Fahie wrote on electrical telegraphy, the first being a history of telegraphy by wire up through 1837, and then wireless by Hertzian waves.
As for Marconi, I have more to say about him later.