The Gravitational Radius, also known as Schwarzschild Radius

Defined by German astronomer, Karl Schwarzschild the gravitational radius is the distance that defines the size at which a spherical astronomical object such as a star becomes a black hole. A black hole is an object so dense that not even light can escape the pull of its gravitational force. If an object collapses to within its Schwarzschild radius, it becomes a black hole. Karl Schwarzschild derived the first model of a black hole in 1916.

Nothing, not even a particle moving at the speed of light, can escape the gravitational pull of a black hole. Therefore, the Schwarzschild radius is the largest radius that a body with a specific mass can have and still keep light from escaping. The formula for the Schwarzschild radius of a body is R_s = GM/c², where R_s is the Schwarzschild radius of the body, G is a constant known as the universal constant of gravitation, M is the mass of the object, and c is the speed of light.

Paper – its historical development

Paper has been traced to China in about AD 105. It reached Central Asia by 751 and Baghdad by 793, and by the 14th century there were paper mills in several parts of Europe. The invention of the printing press in about 1450 greatly increased the demand for paper, and at the beginning of the 19th century wood and other vegetable pulps began to replace rags as the principal source of fiber for papermaking.

The word paper is derived from the name of the reedy plant papyrus, which grows abundantly along the Nile River in Egypt. In ancient times, the fibrous layers within the stem of this plant were removed, placed side by side, and crossed at right angles with another set of layers similarly arranged. The sheet so formed was dampened and pressed. Upon drying, the gluelike sap of the plant, acting as an adhesive, cemented the layers together. Complete defibring, an indispensable element in modern papermaking, did not occur in the preparation of papyrus sheets. Papyrus was the most widely used writing material in ancient times, and many papyrus records still survive.

Bruno Giardano (1548-1600) – proposed an infinite universe

Italian philosopher, astronomer, mathematician, and occultist whose theories anticipated modern science. The most notable of these were his theories of the infinite universe and the multiplicity of worlds, in which he rejected the traditional geocentric (or Earth-centred) astronomy and intuitively went beyond the Copernican heliocentric (Sun-centred) theory, which still maintained a finite universe with a sphere of fixed stars. Bruno is, perhaps, chiefly remembered for the tragic death [his tongue in a gag, and burned alive] he suffered at the stake because of the tenacity with which he maintained his unorthodox ideas at a time when both the Roman Catholic and the Reformed churches were reaffirming rigid Aristotelian and Scholastic principles in their struggle for the evangelization of Europe….

Bruno's theories influenced 17th-century scientific and philosophical thought and, since the 18th century, have been absorbed by many modern philosophers. As a symbol of the freedom of thought, Bruno inspired the European liberal movements of the 19th century, particularly the Italian Risorgimento (the movement for national political unity). Because of the variety of his interests, modern scholars are divided as to the chief significance of his work. Bruno's cosmological vision certainly anticipates some fundamental aspects of the modern conception of the universe; his ethical ideas, in contrast with religious ascetical ethics, appeal to modern humanistic activism; and his ideal of religious and philosophical tolerance has influenced liberal thinkers. On the other hand, his emphasis on the magical and the occult has been the source of criticism as has his impetuous personality. Bruno stands, however, as one of the important figures in the history of Western thought, a precursor of modern civilization. 

(Britannica Encyclopedia)

Salt and blood pressure

Let's now pause for a quick crash course on blood pressure and hypertension, to help you understand what those numbers mean when your doctor inflates a rubber cuff about your arm, listens, deflates the cuff, and finally pronounces, "Your blood pressure is 120 over 80." Blood pressure is expressed in units of millimeters of mercury: the height to which your blood pressure would force up a column of mercury in case, God forbid, your artery were suddenly connected to a vertical mercury column.

Naturally, your blood pressure changes throughout each heart stroke cycle: it rises as the heart squeezes, and it falls as the heart relaxes. Hence your physician measures a first number and then a second number (e.g., 120 and 80 millimeters of mercury), referring respectively to the peak pressure at each heartbeat (called systolic pressure) and to the minimum pressure between beats (termed diastolic pressure). Blood pressure varies somewhat with your position, activity, and anxiety level, so the measurement is usually made while you are resting flat on your back and supposedly calm. Under those conditions, 120 over 80 is an average reading for Americans. There is no magic cut-off between normal blood pressure and high blood pressure. Instead, the higher your blood pressure, the more likely you are to die of a heart attack, a stroke, kidney failure, or a ruptured aorta. Usually, a pressure reading higher than 140 over 90 is arbitrarily defined as constituting hypertension, but some people with lower readings will die of a stroke at age 50, while others with higher readings will die of a car accident in otherwise good health at age 90.

Environmentalism in the United States

The first federal environmental act was the establishment of Yellowstone National Park in March 1872 in the territories of Montana and Wyoming. Instead of promoting the land for development, Congress and President Ulysses S. Grant declared that it should be "as a public park or pleasuring ground for the benefit and enjoyment of the people." As the first such preserve in the world, Yellowstone inaugurated an international national park movement that currently includes some 1,200 parks or preserves in 100 countries, including 391 in the United States.

The Scottish naturalist John Muir became an early advocate for preservation after his travels and scientific work convinced him that some natural areas need protection from human exploitation. Muir founded the Sierra Club in 1892 to that end and urged President Theodore Roosevelt to join the cause. Roosevelt, himself known as an ardent outdoorsman, eventually dedicated more than 150 million acres to national parks and forests, and founded the US. Forest Service, which manages forests for water and timber resources while protecting them for wildlife and recreation. The first chief of the Forest Service, Gifford Pinchot, promoted a "wise use" strategy of wilderness management that proposed, in contrast to Muir, that nature could be safely commercialized.