Today, we fire a shot, and it's heard round the
world. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
If you're my age, you'll
remember an old song lyric:
How deep is the ocean? How high is the
sky?
Well, I'll tell you how deep and how high. Relative
to your 16-inch globe, the ocean is no deeper than
the layer of blue paint that represents it. The sky
reaches only 1/32 of an inch above the surface. Our
water and air are so thin and fragile!
That brings us to the question of global warming.
When the composition of our thin atmosphere
changes, the flow of solar energy through it
changes just a little. Yet it's enough to affect
the ocean -- that mere layer of paint upon our
Earth.
So if we could measure overall changes in the
ocean's temperature, we'd know how much warming has
occured. People at the Scripps Institution in La
Jolla are trying to do that. And they're using the
thinness of the ocean.
The ocean averages a little over two miles deep.
The density of its water varies with depth. The
salinity, temperature, and pressure all change. And
they change the density. Finally, the density of
water determines how sound travels through it.
Those density variations do a strange thing to the
spread of sound in the ocean. Sounds go out in all
directions in air. But sound that originates at a
particular ocean depth spreads only outward. Sound
stays in a plane, if it has a certain density
pattern. Sound also travels five times faster in
water than in air. And it doesn't attenuate as
fast.
So they'll lower a loudspeaker near an island in
the South Indian Ocean. They'll broadcast a
low-frequency tone. Listening posts will pick up
the sound three hours later, when it reaches all
the way to America. It'll be very weak but still
perceivable. Understand: this is no radio signal.
It's pure acoustic sound. We'll literally hear
halfway round the world.
The precise speed of the sound reflects a global
average temperature in the ocean. By doing the
experiment each year, we'll find out how much Earth
is really warming.
The experiment bends my mind. It stretches my
perception of both size and sound. The oddest
wrinkle of all is that this stratum in the ocean is
a communications channel for whales. They use it to
sing to each other over huge distances. We've
already garbled the channel with submarine noise
and geophysical soundings. Now this! There's a
danger that this strange experiment will interfere
with the whales' party line.
Finally, you won't believe the name of the island
that's going to be heard all the way to America.
It's name is H-E-A-R-D -- Heard Island.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
