Early ears, audible plants, and bizarre acoustic experiments through the years - Hindustan Times
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Early ears, audible plants, and bizarre acoustic experiments through the years

ByAnesha George
Apr 12, 2024 05:46 PM IST

Humans have been fascinated by who can hear, and how, for centuries. We’ve used endearing, intriguing and brutal methods to study how sound works.

Early experiments with sound were, by default, linked to music.

Charles Darwin played a bassoon to a mimosa, to test whether plants could “hear”. He wanted to see if it would close its leaves, as it did when touched. (It didn’t.) Above, a recreation of the experiment, by Midjourney. PREMIUM
Charles Darwin played a bassoon to a mimosa, to test whether plants could “hear”. He wanted to see if it would close its leaves, as it did when touched. (It didn’t.) Above, a recreation of the experiment, by Midjourney.

The Greek mathematician and philosopher Pythagoras discovered, in the 6th century BCE, that harmony could also be a matter of math. There are ratios at play that indicate (or determine, who can say) which notes sound best together, when played on certain instruments. (Click here for a bit more on this.)

About 1,000 years later, in the 16th century, the modern study of waves and acoustics began, with Italian astronomer, mathematician and philosopher Galileo Galilei exploring the relationship between the pitch of a taut string and its vibrating length.

It wasn’t until the late-17th century that the French physicist Joseph Sauveur first suggested the name acoustics for the study of sound, separating it and calling it “a science superior to music”.

But hearing, of course, goes back to early life on the planet. The first organisms to “hear” were single-celled aquatic life forms from hundreds of millions of years ago. They evolved tiny hair-like structures called cilia that allowed them to sense the vibrations and movement of other organisms in water, and this ability was passed down to ancient fish.

When life left the water, hearing on land presented new challenges. Palaeontological data indicates that the ear drum most likely evolved in the Triassic period, about 100 million years after the first vertebrates walked on land. The drum made it easier to hear sounds propagated through the air; evolving the ability to hear such sounds more keenly could mean the difference between survival and extinction.

Humans have been fascinated by who can hear, and how, for centuries. And there is some brutal history to the way we’ve studied sound.

Let’s start out with something lighter. Charles Darwin tried to find out if plants could “hear” by playing a bassoon to a mimosa, wondering if it would close its leaves in response as it did when touched. He later went on to call it a “fool’s experiment” but studies since have shown that sounds played repeatedly over long periods can induce plants to germinate and grow slower or faster.

This isn’t strictly hearing; it is sensitivity to vibrations. Plants do use “sound”, however. They locate water and grow towards it, for instance, based on the vibrations caused as water moves through earth, or through a pipe.

Now to the rougher stuff. In 1793, the Italian priest and biologist Lazzaro Spallanzani surgically blinded bats, removing their eyeballs to see if they could really still fly past obstacles in the dark.

When they continued to do so with relative ease, he plugged their ear canals, which led them to collide with objects in their path. Spallanzani didn’t learn much from this either. It would be another 150 years until the term echolocation was coined, in 1944, by a 29-year-old zoologist named Donald Griffin.

A particularly delightful experiment in sound, meanwhile, proved that a certain pitch can put out a fire.

It all began in 1912, when American naturalist Charles Kellogg, known for his mimicry of birdsongs, announced that he could extinguish flames by drawing the bow of a violin across a tuning fork. The scientific community reportedly did not know what to make of his demonstrations then. But over 100 years later, in 2015, two engineering students at George Mason University in Virginia, Viet Tran and Seth Robertson, managed to create a fire extinguisher as part of their senior research project that operates in just the same way.

They found that sounds that are emitted as pressure waves, in the right frequency (a bass range of 30 to 60 Hz), can reliably put out small fires, as they displace oxygen from the area near flames and fuel. There has been no talk of commercial application; one would presumably feel a bit foolish trying to size up a fire and determine whether to pull up a playlist or reach for an extinguisher.

Perhaps it is incredible enough that it works.

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