Jason Crawford

And you'd fill it up with steam and then you would spray cold water into the piston, which would condense the steam rapidly, form a vacuum.

And then the outside air pressure would actually push the piston down against the vacuum.

Later versions of the steam engine used high pressure steam and the steam itself would actually push the piston.

And in fact, there were versions that pushed it in both directions.

So you'd get high pressure steam on one side than the other and so forth.

But that's not how the earliest steam engines worked.

They worked by creating a vacuum.

So you needed to have, to create this, you needed some idea that vacuums existed and that air pressure existed and could push against the vacuum and actually push the pistons.

And that science was worked out, in fact, in the 1600s.

So it was, I believe, Evangelista Torricelli, the Italian scientist who first demonstrated in the 1640s that the air has weight.

In the 1650s, a famous demonstration was done called the Magdeburg Hemispheres.

They are illustrated here at the top.

Two hemispheres of metal, I believe they're made of copper, that could be pressed together.

And then the air pumped out of them.

So they had air pumps at this time.

And they could create vacuums in sealed chambers with an air pump.

So these two chambers, these two halves were placed together to form a sealed chamber.

The air pumped out of them.

And then let's zoom in on the middle here so you can see what's going on.

They actually tied a team of horses to each half and strained at the hemispheres to try to pull them apart with all of the traction of these horses.