Antonie van Leeuwenhoek

Antonie Philips van Leeuwenhoek was a Dutch businessman and scientist in the Golden Age of Dutch science and technology. A self-taught man in science, he is known as "the Father of Microbiology", one of the first microscopists and microbiologists. Van Leeuwenhoek is best known for his pioneering work in microscopy and for his contributions toward the establishment of microbiology as a scientific discipline. Raised in Delft, Dutch Republic, van Leeuwenhoek worked as a draper in his youth and founded his own shop in 1654, he developed an interest in lensmaking. In the 1670s, he started to explore microbial life with his microscope; this was one of the notable achievements of the Golden Age of Dutch discovery. Using single-lensed microscopes of his own design, van Leeuwenhoek was the first to experiment with microbes, which he referred to as dierkens, diertgens or diertjes. Through his experiments, he was the first to determine their size. Most of the "animalcules" are now referred to as unicellular organisms, although he observed multicellular organisms in pond water.

He was the first to document microscopic observations of muscle fibers, spermatozoa, red blood cells, crystals in gouty tophi, blood flow in capillaries. Although van Leeuwenhoek did not write any books, his discoveries came to light through correspondence with the Royal Society, which published his letters. Antonie van Leeuwenhoek was born in Delft, Dutch Republic, on 24 October 1632. On 4 November, he was baptized as Thonis, his father, Philips Antonisz van Leeuwenhoek, was a basket maker who died when Antonie was only five years old. His mother, came from a well-to-do brewer's family, she remarried a painter. Antonie had four older sisters: Margriet, Geertruyt and Catharina; when he was around ten years old his step-father died. He attended school in Warmond for a short time before being sent to live in Benthuizen with his uncle, an attorney. At the age of 16 he became a bookkeeper's apprentice at a linen-draper's shop in Amsterdam, owned by the Scot William Davidson. Van Leeuwenhoek left there after six years.

Van Leeuwenhoek married Barbara de Mey in July 1654, with whom he fathered one surviving daughter, Maria. That same year he returned to Delft, where he would study for the rest of his life, he opened a draper's shop. His wife died in 1666, in 1671, van Leeuwenhoek remarried to Cornelia Swalmius with whom he had no children, his status in Delft had grown throughout the years. In 1660 he received a lucrative job as chamberlain for the assembly chamber of the Delft sheriffs in the city hall, a position which he would hold for 40 years. In 1669 he was appointed as a land surveyor by the court of Holland. Van Leeuwenhoek was a contemporary of another famous Delft citizen, the painter Johannes Vermeer, baptized just four days earlier, it has been suggested that he is the man portrayed in two Vermeer paintings of the late 1660s, The Astronomer and The Geographer, but others argue that there appears to be little physical similarity. Because they were both important men in a city with only 24,000 inhabitants, it is that they were at least acquaintances.

While running his draper shop, van Leeuwenhoek wanted to see the quality of the thread better than what was possible using the magnifying lenses of the time. He developed an interest in lensmaking. Van Leeuwenhoek's interest in microscopes and a familiarity with glass processing led to one of the most significant, well-hidden, technical insights in the history of science: By placing the middle of a small rod of soda lime glass in a hot flame, van Leeuwenhoek could pull the hot section apart to create two long whiskers of glass. By reinserting the end of one whisker into the flame, he could create a small, high-quality glass sphere; these spheres became the lenses of his microscopes, with the smallest spheres providing the highest magnifications. After developing his method for creating powerful lenses and applying them to the study of the microscopic world, van Leeuwenhoek introduced his work to his friend, the prominent Dutch physician Reinier de Graaf; when the Royal Society in London published the groundbreaking work of an Italian lensmaker in their journal Philosophical Transactions of the Royal Society, de Graaf wrote to the editor of the journal, Henry Oldenburg, with a ringing endorsement of van Leeuwenhoek's microscopes which, he claimed, "far surpass those which we have hitherto seen".

In response, in 1673 the society published a letter from van Leeuwenhoek that included his microscopic observations on mold and lice. Van Leeuwenhoek's work captured the attention of the Royal Society, he began corresponding with the society regarding his observations. At first he had been reluctant to publicize his findings, regarding himself as a businessman with little scientific, artistic, or writing background, but de Graaf urged him to be more confident in his work. By the time van Leeuwenhoek died in 1723, he had written some 190 letters to the Royal Society, detailing his findings in

Iron(II) bromide

Iron bromide is a inorganic compound with the chemical formula FeBr2. The anhydrous compound is a brownish-colored paramagnetic solid. Several hydrates of FeBr2 are known, all being pale colored solids, it is a common precursor to other iron compounds in research laboratory, but no applications exist for this compound. Like most metal halides, FeBr2 adopts a polymeric structure consisting of isolated metal centers cross-linked with halides, it crystallizes with the CdI2 structure, featuring close-packed layers of bromide ions, between which are located Fe ions in octahedral holes. The packing of the halides is different from that for FeCl2, which adopts the CdCl2 motif. FeBr2 is synthesized using a methanol solution of concentrated hydrobromic iron powder, it adds the methanol solvate Br2 together with hydrogen gas. Heating the methanol complex in a vacuum gives pure FeBr2. FeBr2 reacts with two equivalents of tetraethylammonium bromide to give 2FeBr4. FeBr2 reacts with bromide and bromine to form the intensely colored, mixed-valence species −.

FeBr2 possesses a strong metamagnetism at 4.2 K and has long been studied as a prototypical metamagnetic compound

Carroll's paradox

In physics, Carroll's paradox arises when considering the motion of a falling rigid rod, specially constrained. Considered one way, the angular momentum stays constant, it is named after Michael M. Carroll who first published it in 1984. Consider two concentric circles of radius r 1 and r 2 as might be drawn on the face of a wall clock. Suppose a uniform rigid heavy rod of length l = | r 2 − r 1 | is somehow constrained between these two circles so that one end of the rod remains on the inner circle and the other remains on the outer circle. Motion of the rod along these circles, acting as guides, is frictionless; the rod is held in the three o'clock position so that it is horizontal released. Now consider the angular momentum about the centre of the rod: After release, the rod falls. Being constrained, it must rotate; when it gets to a vertical six o'clock position, it has lost potential energy and, because the motion is frictionless, will have gained kinetic energy. It therefore possesses angular momentum.

The reaction force on the rod from either circular guide is frictionless, so it must be directed along the rod. Taking moments about the center of the rod, there can be no moment acting on the rod, so its angular momentum remains constant; because the rod starts with zero angular momentum, it must continue to have zero angular momentum for all time. An apparent resolution of this paradox is. To maintain the rod in a radial position the circles have to exert an infinite force. In real life it would not be possible to construct guides that do not exert a significant reaction force perpendicular to the rod. Victor Namias, disputed that infinite forces occur, argued that a finitely thick rod experiences torque about its center of mass in the limit as it approaches zero width. Carroll, Michael M.. "Singular constraints in rigid-body dynamics". American Journal of Physics. 52: 1010–1012. Bibcode:1984AmJPh..52.1010C. doi:10.1119/1.13777. Namias, Victor. "On an apparent paradox in the motion of a smoothly constrained rod".

American Journal of Physics. 54: 440–445. Bibcode:1986AmJPh..54..440N. Doi:10.1119/1.14610. Felszeghy, Stephen F.. "On so-called singular constraints in rigid-body dynamics". American Journal of Physics. 54: 585–586. Bibcode:1986AmJPh..54..585F. Doi:10.1119/1.14533