A/C hasn't only made life cooler

As a heat wave hits America from coast to coast, it’s hot outside – but cool inside, thanks to the triumph of air conditioning.

For most of human history, there was little people could do to avoid heat.

During the day, it drove people outside of their homes to enjoy the shade of a tree or to take a refreshing dip in a lake or river.

At night, folks in cities slept outside on their porches, roofs a...