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Bridging rivers, gorges, narrows, straits, and valleys always has played an important role in the history of human settlement. Since ancient times, bridges have been the most visible testimony of the noble craft of engineers. A bridge can be defined in many ways, but Andrea Palladio, the great 16th century Italian architect and engineer, hit on the essence of bridge building when he said "...bridges should befit the spirit of the community by exhibiting commodiousness, firmness, and delight." In more practical terms, he went on to explain that the way to avoid having the bridge carried away by the violence of water was to make the bridge without fixing any posts in the water. Since the beginning of time, the goal of bridge builders has been to create as wide a span as possible which is commodious, firm, and occasionally delightful. Spanning greater distances is a distinct measure of engineering prowess.

Science & Society Picture Library represents the collections of the National Museum of Science & Industry, Science Museum, National Museum of Photography, Film & Television, National Railway Museum.

This is a dictionary of algorithms, algorithmic techniques, data structures, archetypical problems, and related definitions. Algorithms include common functions, such as Ackermann's function. Problems include traveling salesman and Byzantine generals. Some entries have links to implementations and more information. Index pages list entries by area and by type. The two-level index has a total download 1/20 as big as this page.

On June 23 1794, Robert Baldry and Richard Randall drew up an agreement for the building of "a new and substantial Bridge of brickwork over the River or Rivulet dividing the parishes of Ubbeston and Heveningham at and for the sum of seventy-six pounds". The two men were the Surveyors of Ubbeston, responsible for the supervision of all buildings within the village, and Robert Baldry was especially well placed to oversee this particular work since he had built the present Old Rectory for his own use eighteen years before (his initials can still be see on the chimney stack).

Am I pregnant? The answer to this age-old question once demanded a combination of guesswork, intuition, and time. In 1978, however, the long wait to know for sure became a thing of the past. Trumpeted by advertisements as “a private little revolution,” the first home pregnancy tests started appearing on drug store shelves that year. A quarter of a century later, innovations promise to make even the telltale thin blue line obsolete. This web site looks at the history of the home pregnancy test—one of the most ubiquitous home healthcare products in America—and examines its place in our culture.

The home pregnancy test works by identifying the presence of the “pregnancy hormone,” human chorionic gonadotropin (hCG), in urine. Research that led to a sensitive, accurate test for hCG was done by scientists in the Reproductive Research Branch of the National Institute of Child Health and Human Development at NIH.

Before we continue describing the evolution of ways to mark the passage of time, perhaps we should broadly define what constitutes a clock. All clocks must have two basic components:

a regular, constant or repetitive process or action to mark off equal increments of time. Early examples of such processes included the movement of the sun across the sky, candles marked in increments, oil lamps with marked reservoirs, sand glasses (hourglasses), and in the Orient, knotted cords and small stone or metal mazes filled with incense that would burn at a certain pace. Modern clocks use a balance wheel, pendulum, vibrating crystal, or electromagnetic waves associated with the internal workings of atoms as their regulators.

a means of keeping track of the increments of time and displaying the result. Our ways of keeping track of the passage of time include the position of clock hands and digital time displays.

The history of timekeeping is the story of the search for ever more consistent actions or processes to regulate the rate of a clock.

We provide information about the history of Federal efforts devoted to public health, preserve and interpret the history of PHS, and promote historically-oriented activities across the U.S. Department of Health and Human Services, in partnership with the History Office of the Food and Drug Administration and the National Institutes of Health Historical Office.

Throughout the last three thousand years, smallpox has shadowed civilization. A viral infection, the disease spread along trade routes, emerging first in Africa, Asia and Europe and reaching the Americas in the sixteenth century. Because smallpox requires a human host to survive it tended to smolder in densely populated areas, erupting in a full-blown epidemic every ten years or so.

Wherever it appeared, the legacy of smallpox was death, blindness, sterility and scarring.

While some medical practitioners claimed to cure smallpox, most medical traditions focused on prevention. Quarantining smallpox patients often limited the spread of the disease and was commonly used even into the twentieth century as there is no cure for smallpox.

The online presentation of The Wilbur and Orville Wright Papers at the Library of Congress, comprising about 10,121 library items or approximately 49,084 digital images, documents the lives of Wilbur and Orville Wright and highlights their pioneering work which led to the world's first powered, controlled and sustained flight. Included in the collection are correspondence, diaries and notebooks, scrapbooks, drawings, printed matter, and other documents, as well as the Wrights' collection of glass-plate photographic negatives. The Wright Brothers' letters to aviation pioneer and mentor Octave Chanute, from the Octave Chanute Papers, were also selected for this online collection. The Wright Papers span the years 1881 to 1952 but largely cover 1900 to 1940. This online presentation includes the famous glass-plate negative of the "First Flight" at Kitty Hawk on December 17, 1903, as well as diaries and letters in which Wilbur and Orville Wright recount their work that led to that day.

Goddard Space Flight Center Library

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