Tension is building between the Aztecs and the Spaniards, not to mention within Cortés's own ranks. Despite this, the conquistador rallies his troops to conquer Mexico.

Cortés sets out to conquer Mexico with his four hundred men, sixteen horses, and seven cannons. He is joined later by native forces, the Totonac warriors.

The Maestro explains how the revolutionary ideas of the early discoverers, which we now take for granted, were not always well received. Before Galileo, for example, everyone believed that the sun and all the other planets revolved around the earth!

In this video, a young Galileo gets one of his first revolutionary ideas on how to measure time. Pretty impressive for a fourteen-year-old, huh?

Episode nine of this series focuses on Galileo, a prolific inventor and scientist. He discovered the principle of the simple pendulum motion, very useful in the measure of time and later in the making of clocks.

In part four of this episode on "The Discoverers," Galileo, now a reputable scholar at the University of Padua, proceeds to make a telescope out of lenses with the help of his instrument maker, Marc'Antonio. In this cartoon, an attempt is made to explain Galileo's discoveries.

In part five of this episode on "The Discoverers," Galileo is warned. His belief that the Earth revolves around the sun is sacrilegious. Giordano Bruno, who claimed this fact, was burned as a heretic by the Inquisition Tribunal.

Galileo is about to throw caution to the wind and reveal his startling discoveries about planet Earth.

Galileo is under close scrutiny because of his Copernican views. Unfazed, he carries on his research and his teachings. Will the Inquisition bring his demise or will his powerful friends, Pope Urban VIII among them, protect him?

Galileo faces an uncertain future. Behind the scenes are political and religious intrigues and enemies plotting his downfall. The Pope, until now sympathetic to Galileo, has a change of heart. Under pressure from all sides and insulted by his latest works, The Dialogue Concerning the Two Chief World Systems, portraying the Church's view through the character Simplicio (Simpleton), the pope finally sends Galileo to the Inquisition Tribunal.

Galileo is in prison. He tries one more time to prove his theories to his inquisitor. But he finally recants during the trial saying the famous sentence: "and yet... it turns"

In the series "Once Upon a Time... the Discoverers," the Maestro lets off some steam. Some two thousand years ago, Heron invented the steam machine in Alexandria, but it took two millenia to perfect the invention and put it to practical use.

In part two of this series, "Once upon a Time... the Discoverers," Maestro talks about Cugnot, the inventor of the steam traction engine.

Years of research and trial and error culminated in the invention of the first locomotive on rails. Not bad for a father-and-son experiment. That's what Murdoch and his son George achieved in 1797.

George Stephenson tries out his invention, a steam locomotive. He allows his son, Robert, to ride on it as long as he stays on the edge of the carriage and gets ready to jump off if the rails buckle under the weight of the locomotive... which they do. Luckily his son followed his instructions!