In 1951, the physicist Paul A.M. Dirac called for the re-introduction of the æther in an oft-quoted letter to Nature. His was an attempt to resuscitate an epistemic object that most scientists at the time, as much as today, judged to be dead and buried. By using the old-fashioned spelling, Dirac was making a statement […]
Syphilis is a sexually transmitted disease caused by a spirochete, a bacterium, Treponema pallidum subspecies pallidum . The main route of infection is by sexual contact but is also transmitted from the mother to the newborn in what is known as congenital syphilis. If syphilis is left untreated for years the treponema may invade the […]
November 25, 1858, was a very cold day in Concord, Massachusetts. It was then that Henry David Thoreau discovered at Walden Pond some frozen fish he had never seen before, which were “shaped like bream, but had the transverse bars of perch”, as he wrote the following day. “Are they not a new species?” he […]
It is said that Washington Irving’s biography of Christopher Columbus, published in 1828, was the work that started the legend that the discoverer of America was the person that convinced the ‘nearly medieval’ Europeans of his time of the sphericity of the earth, a legend that has captured the popular imagination since then. Nothing could […]
A 1 million-year-old fire lit by human ancestors was discovered in 2012 in the Wonderwerk Cave in South Africa. The soil of the cave yielded several dozen stone tools, microscopic plant ashes and burned bone bits. It is supposed that a member of the Homo genus, perhaps Homo erectus , made a fire that produced […]
The success of Bohr’s model of the atom in accounting for the spectrum of hydrogen left this question: Could experiments show directly that atoms do have only certain, separate energy states? In other words, are there really gaps between the energies that an atom can have? A famous experiment in 1914, by the German physicists […]
The idea that the solution of Schrödinger’s equation is a wave that represents, not a physical wave, but the probability of finding the associated particle in some specific condition of motion has had great success. In fact, every experiment devised so far to test this interpretation has confirmed these results. Yet many scientists still find […]
By the mid-1920s it was clear that “things” (electrons, atoms, molecules) long regarded as particles also show wave properties. This fact is the basis for the currently accepted theory of atomic structure. This theory, quantum mechanics, was introduced in 1925. Its foundations were developed very rapidly during the next few years, primarily by Born, Heisenberg […]
He was a man of insatiable curiosity and a hallmark of modern multidisciplinarity. Yet he was born on an April day six centuries ago. He never attended university, and still he authored masterpieces in the history of art and cultivated a broad range of interests and skills. Distant domains such as painting, sculpture, technology and […]
We recently explored the concepts that Faraday introduced regarding the relationship between electricity and magnetism. In this article we focus on their treatment by Maxwell. The work of Oersted, Ampere, Henry, and finally Faraday had established two basic principles of electromagnetism: 1. An electric current in a conductor produces magnetic lines of force that circle […]