"If you saw a heat wave, would you wave back?"
~ Stephen Wright
Walking is a muse and a madeleine for me — it stirs up new ideas and old memories. I walk three or four miles almost every day, but some days are easier than others.
Yesterday, when I set out for a walk at 10 a.m., the temperature was already in the high 80s. As I walked, the heat was set on broil; it burned down from above and smoldered up from the pavement in a fiery feedback loop. The tar on the street was already beginning to turn gummy. It crossed my mind that on relentlessly sunny days like this, every little pool of shade becomes an oasis.
Photo courtesy of New York City Regional Center
The thought of an oasis led me to a distant memory of another hot day when I was around three years old. I was in a car, transfixed by highway mirages — the sparkling pools of "water" that appear and disappear on the road ahead.
When I asked about them, I was told they were a trick of the light or the eye. That answer alerted me to the notion that sight and light are unreliable narrators, but it didn't help me understand what I was seeing — or more accurately, not seeing. The photo above is from NASA's Earth Science Picture of the Day website, which offers the succinct explanation I yearned for as a child. Here it is:
"The effect is caused by a thin layer of hot air just above the ground. The difference in refractive index between the hot air at the road surface and the denser, cooler air above it causes the boundary to act like a mirror: distant objects are reflected...The 'water' is actually a reflection of the blue sky, but a close look at this image also shows reflections of a car, power poles, bushes, a mile marker, and roadside grass. Because the reflection occurs solely at very shallow angles, the mirage appears only in the distance and continually recedes as one moves towards it."
I saw no highway mirages yesterday, but the heat wave isn't done with us yet. I'll keep looking.
"Our knowledge is a receding mirage in an expanding desert of ignorance."
~ Will Durant