Why Does Rain Smell and More Questions From Our Readers

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Why do domestic cats have slit-shaped pupils and large cats, such as lions and tigers, have round pupils?
Renee Spears
Forest Grove, Oregon

It’s because small cats are more active at night than big ones. Their pupils have evolved to open wide in low light, but to contract to narrow slits in sunlight or in bright artificial light so they aren’t blinded.
John Seidensticker
Conservation Scientist, National Zoo

When the British burned the Library of Congress during the War of 1812, did they destroy books once owned by Thomas Jefferson?
Gary Miller
Davenport, Florida

No. It was that fire, on August 24, 1814, that motivated Jefferson to sell the United States his library—the largest private collection in the country—to replace what had been lost. But then an 1851 fire destroyed most of those books. The Library of Congress has reconstructed Jefferson’s library and placed it on exhibit in its Jefferson Building.
Nancy Gwinn
Director, Smithsonian Libraries

Why does rain have a distinctive smell?
Manisha Sekaran
Klang, Malaysia

That smell has several components. Before a storm arrives, we may smell ozone in the downdraft from approaching thunderheads. After it arrives, we smell oils, plant spores and other earthly and botanical chemicals that are released by pelting rain. Rainwater tends to be somewhat acidic, and these acids react with bacteria and botanical substances to create new compounds and release new scents. So the smell of rain is an “earthy” smell that speaks of plant growth. Some scientists speculate that we are conditioned to like it because it heralds the bounty of the earth.
Douglas Herman
Geographer, National Museum of the American Indian

A modern medical mystery

Do scholars know when the greatest number of languages were spoken, and how many there were?
Bob Jackson, Cartersville, Georgia

No, on both counts. There is no data at all for most of the languages spoken in the past, even assuming we could determine what to count as a separate language. And writing—historically the primary means of preserving language—is very recent in human history and extremely recent in the parts of the world with the most languages.
Ives Goddard
Linguist, National Museum of Natural History

When someone loses 100 pounds, where does all that weight go?
Rachel Berndt, Minneapolis, Minnesota

If you think in planetary terms, it doesn’t go anywhere. That weight represented stored energy; when that energy was “burned,” the chemical combustion produced energy plus some waste products. Both the energy and the waste remain part of the earth’s environment.
David DeVorkin
Senior Curator, National Air and Space Museum

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