Atlantean engineers would have improved the device. Further improvements could have led to flight, using the electromagnet to get a glider off the ground and then launching it by hand or catapult or some other device. Copper could have held the electromagnetic charge for later use in some other device, leading to the primitive battery-like devices that have been discovered. Yet above all, the Atlantean engineers, who had stumbled across this great discovery by complete accident, would never let anyone get a good enough look at the device to try and re-create it. The secret of the Atlantean antigravity machine and flying machines would have been kept on the island itself.
Yet no evidence of this exists in Greece. This would make sense. Even if the war had been settled by the time the Atlanteans crafted their first aircraft (or perhaps this was the reason the war was settled, either due to Athenian fear of Atlantean aircraft or the desire of the Atlanteans to devote all their time to researching this new invention), the people of the great island would have been hesitant to share their greatest secret with those who were their enemies. Yet their friends and allies, the people of Egypt and Carthage - potential enemies of an expanding Greek Empire - would have reaped benefits and helped in the research of the device. This would explain the relics in Egypt that suggest flight and the regions of the Inca farmlands that were converted into giant symbols facing the skies.
But like all civilizations when given power, the Altanteans would have eventually been corrupted. They had, after all created the device and improved upon it; why could they not do so again? Make it even more powerful and who knows what they could reap? They could rule the world; more, even, the might be able to rule the stars! Perhaps they discussed this with other civilizations, as a project of this magnitude would have taken many years to complete; this could be where the plans of what appear to be space ships came from. It would also explain the images of great aerial battles and seemingly bombed-out villages; the Atlanteans became power-hungry and began to fall into the trap of humanity: They wanted to rule the world.
But the Atlanteans messed up. They took their obsession with the antigravity device too far. Another thing that electromagnets do that no Atlantean could have seen coming is it affects the weather. A sudden, powerful electromagnetic activation triggered a cataclysmic storm to descend on the island of Atlantis. The waves crushed the sea wall and ripped the great island apart, crushing it down into the depths of the ocean.
Yet the Atlanteans would not have been stupid. They would have tried to save their device, protect their legacy; to that end, they placed the device on one of their ships, trying desperately to get it to safety. No port in the Mediterranean could be trusted, not after the war with Athens (the second most powerful naval force in the Mediterranean Sea); the only safe harbor for the prized Atlantean device would have been the colonies of Bermuda and Bimini.
Yet the storm would have followed them, following the electromagnetic current. As the outer storm clouds licked the edges of the colonies, the fleet carrying the device sank. The storm, combined with rising tide levels due to the electromagnet, would have swamped the islands.
After the tragedy, no one in the Mediterranean would have again tried to fly or build the great device, seeing the destruction of the island, no doubt, as the wrath of angry gods. Surviving Atlanteans on Easter Island would have set sail for mainland where they could find both food and shelter, possibly believing that their god Poseidon had turned against them. Their statues remain to this day, watching for the return of the Atlantean colonists to the island. Those colonists, of course, will never return; the Spanish conquistadores would have seen to that, however inadvertently. With no surviving Atlanteans and no records of them besides tales and Plato, Atlantis would have dissolved into myth.
Let's take a quick breather here and examine that last statement. During the time of Atlantis, there were several powerful civilizations. Greece, which speaks of Atlantis by name. Egypt, which speaks of Atlantis by name via Plato and has much of its history buried in the pyramids. Carthage, which was burned to the ground and totally annihilated by Rome; no surviving documents. The Inca, who have no surviving history. The Maya, who have no surviving history. The Aztecs and the natives of North America are mostly the same, but those that do have surviving tales and records tell of the great island nation of Atlan. The African tribes, some of whom tell a tale of a great Atlantic island nation. Every major civilization of the time of Atlantis either has no surviving records or speaks of Atlantis in some form!
