Q: Why don’t people smile in old photographs?

— Art Ross | Kingwood, Texas

Although we tend to think the subjects had to hold their faces still for an uncomfortably long time, exposures from the early days of commercial photography only lasted about 5 to 15 seconds. The real reason is that, in the mid-19th century, photography was so expensive and uncommon that people knew this photograph might be the only one they’d ever have made. Rather than flash a grin, they often opted to look thoughtful and serious, a carry-over from the more formal conventions of painted portraiture, explains Ann Shumard, senior curator of photographs at the National Portrait Gallery. When George Eastman, founder of Eastman Kodak, introduced hand-held cameras in 1888, it made photography more accessible and casual. Photos from around the turn of the 20th century include a lot more candids, and a lot more smiles.

Q: Which animals have the best distance vision? Do animals experience near-sightedness and far-sightedness?

— Laura Beamer | New York City

Rhinos and bats tend to be near-sighted, but they make up for it with superior hearing. Owls and eagles have the best vision; the latter can see distant objects eight times better than humans. While there might be individual animals that see worse than others in their species, survival of the fittest tends to weed them out. Steven Sarro, a supervisory biologist and curator at the National Zoo, says an owl with bad vision won’t last long in the wild. Unlike a human, it can’t fall back on glasses or Lasik surgery.

Q: When did Americans start to worry that foreigners were interfering with U.S. politics?

— Anonymous

In the earliest days of the Republic, says Jon Grinspan, a curator at the National Museum of American History. During the French Revolution, a faction of conservative, pro-English Americans worried that radical Jacobins—who were beheading their compatriots in Paris—would try to meddle in U.S. politics. That fear led to the 1798 passage of the Alien and Sedition Acts, which, among other things, tightened restrictions on criticism of the government and loosened those on deportation of non-citizens. The fear of meddling rose next in the 1840s, when the anti-immigrant and anti-Catholic Know-Nothing Party saw new immigrants from Ireland as part of a papal plot to take over America.

Q: Why did the Vikings, who lived in Greenland alongside the Inuit for several hundred years, not spread European diseases like the Spaniards did several hundred years later?

— Phyllis Schmutz | Nesconset, New York

Location, for the most part, says William Fitzhugh, director of the Smithsonian’s Arctic Studies Center. When the Norse arrived in 985, and until they left in the 1450s, they settled on the southwest coast of Greenland, far away from where any proto-Inuit people lived. Starting around 1350, the proto-Inuit Thule people migrated to this region. But unlike in the Americas, where trade was frequent, there was minimal interaction and no cohabitation between Europeans and indigenous people in Greenland. European diseases, like measles and tuberculosis, made their way to Greenland in the 17th and 18th centuries, as Denmark started to colonize the island.

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