Well, now we have a cold body that also is specific for conduction. In other words, when this piston moves this way, there's an increase in temperature. And the increase in temperature causes energy to transfer via conduction from this place to this place. And this makes the temperature stay constant. Okay, so the final outcome is that a heat engine needs to look like this. A heat engine needs to have a hot body, a cold body, a cylindrical tube, as well as a piston that's controlled by some outside force.