It's safe to say that as you read this on an August West Texas day, you're in an air conditioned building.  But the air conditioner as we know it didn't come about until the 1920s.  And as late as 1965 only 10% of American homes had air conditioning (87% have it today).

How did our grandparents live without it?
They did it in several ingenious ways:
House on Blocks
Have you noticed many older homes aren't on slabs but instead are built off the ground?  That's so air could flow underneath the house, helping to keep it cool.
Tall Ceilings
Again, notice all the cool, tall ceilings in old houses?  That isn't just for dramatic affect.  It's also so the warm air would collect up high.
Ceiling Fans
The fans predated air conditioning and were introduced with the availability of electricity.
Transoms
You don't see these much anymore.  But this was a small window above the door that could be opened to allow air to flow through the house but still allow for privacy and security.
Porches
Old homes seem more likely to have those big, wraparound porches that are so nice to sit on a warm Texas evening!  These allowed light to come in the house but not get the direct, hot sun.  People also would sleep outside in these screened in porches for the cool nights without getting bitten by bugs.
Reflective Roofs
That cat was on a hot tin roof because tin and other light-colored metals would reflect sunlight, helping to keep the house cool.  Now we have dark shingles that absorb sunlight.  Why is that?
Thick Walls
Europe still builds their houses this way.  This was especially common in the southern United States.  12-24 inch walls that would block the heat during the day and retain the warmth at night.