How Many Stradivariuses Exist and More Questions From Our Readers

Can marine invertebrates, such as octopuses, be induced to use tools? I’ve seen an octopus move an object to barricade itself inside a lair.
Chloe Newcomb
Hodgetts, St. George’s, Bermuda

There’s no consensus on how to define “tool use,” but generally a tool is an object used to manipulate or alter another object. Over more than two decades of observation, we haven’t seen an octopus use an object that way. Moving a shell to use as cover doesn’t qualify because the shell does not alter the object forming the lair.
Alan Peters
Curator, National Zoo

How many instruments did Antonio Stradivari build, and how were they identified or authenticated?
Gisela Randecker
Beatty, Nevada

Stradivari probably built around 1,100 violins, violas and cellos; perhaps 400 to 500 survive, and some are still being played. He added a label bearing his name, his town of Cremona and the year to all his instruments on the inside and visible through the f-hole. Identifying a Stradivarius today may be complicated by the number and nature of repairs made to the instrument since his death, in 1737.
Bruno Frohlich
Anthropologist Museum of Natural History

My family has portraits of distant ancestors William and Elizabeth Gamble Wirt by C.B.J. de St. Mémin. What is their historical significance?
Jonathan Cates
Washington, D.C.

Charles Balthazar Julien Févret de Saint-Mémin (1770-1852) fled the French Revolution in 1793 and lived in the United States for 20 years. He drew almost a thousand chalk portraits using a device called a physiognotrace, which allowed for extra­ordinary accuracy. The Wirt portraits were made in Richmond in 1807, while William Wirt, a lawyer, was helping to prosecute Aaron Burr for treason.
Ellen Miles
Curator of Painting and Sculpture, National Portrait Gallery

How do astronomers determine the ro­tational period of a gas giant such as Jupiter, since the atmospheric bands rotate at different speeds or in different directions?
Tom Welch
Dunwoody, Georgia

They do it with radio telescopes. Like Earth, Jupiter has a stable, dipole magnetic field and a set of radiation belts, similar to Earth’s Van Allen belts. The field and the belts rotate. By measuring changes in emissions from the radiation belts, astronomers deduce the rotation of the magnetic field. And that, they assume, equals Jupiter’s true rotational rate.
Scott Kenyon
Astrophysicist, Harvard-Smithsonian Center for Astrophysics

My father, a Pan Am captain, once got Charles Lindbergh to sign his flight plan. How can I preserve it? Display it?
Robert A. Chamberlain
Wichita, Kansas

Protect it from direct light, heat, humidity, pests, accident or loss by placing it in an acid- and lignin-free archival print folder (and box) or preservation-quality album and store it in a room with a stable climate. It’s always best to frame a good copy, not the original.
Nora Lockshin
Paper Conservator, Smithsonian Institution Archives