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History Lesson: The Magnetic Compass

The navigational instrument made its first appearance in the Mediterranean in the early 14th century

4 min read
Chinese mariners compass, mid 19th century.
Photo: SSPL/Getty Images

THE INSTITUTEInhospitable as it can be, the sea has played an essential role in human history, and so did that indispensible navigation tool, the magnetic compass. The sea provided the cheapest way to move goods over great distances, generating wealth through trade. Navigating the oceans successfully also played a pivotal role for many countries in gaining political and military power. Along the way, the compass contributed to innovations in physics and electrical engineering.

Far from the sight of land, the sea is a seemingly endless, undifferentiated expanse. For most of history, getting lost at sea was a very real danger, often with disastrous consequences. Even when close to land, seafarers can become disoriented in bad weather. For ancient Greek and Roman sailors, weather conditions even limited visibility enough to shorten the sailing season in the Mediterranean Sea. The Roman military writer Publius Flavius Vegetius wrote in the fourth century that travel from June to mid-September was safe, but that sailing any other time was risky. He called the period between mid-November and mid-March mare clausum, or the time when “the seas are closed.”

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Economics Drives Ray-Gun Resurgence

Laser weapons, cheaper by the shot, should work well against drones and cruise missiles

4 min read
In an artist’s rendering, a truck is shown with five sets of wheels—two sets for the cab, the rest for the trailer—and a box on the top of the trailer, from which a red ray is projected on an angle, upward, ending in the silhouette of an airplane, which is being destroyed

Lockheed Martin's laser packs up to 300 kilowatts—enough to fry a drone or a plane.

Lockheed Martin

The technical challenge of missile defense has been compared with that of hitting a bullet with a bullet. Then there is the still tougher economic challenge of using an expensive interceptor to kill a cheaper target—like hitting a lead bullet with a golden one.

Maybe trouble and money could be saved by shooting down such targets with a laser. Once the system was designed, built, and paid for, the cost per shot would be low. Such considerations led planners at the Pentagon to seek a solution from Lockheed Martin, which has just delivered a 300-kilowatt laser to the U.S. Army. The new weapon combines the output of a large bundle of fiber lasers of varying frequencies to form a single beam of white light. This laser has been undergoing tests in the lab, and it should see its first field trials sometime in 2023. General Atomics, a military contractor in San Diego, is also developing a laser of this power for the Army based on what’s known as the distributed-gain design, which has a single aperture.

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