11th Class

"We recognized almost at once that the material was different and that It had potential... “ Lois Plunkett In 1938 research chemist Roy Plunkett (1910-1994) was working at the DuPont Jackson laboratory in New Jersey. He had been trying to improve refrigerants to make them nontoxic and nonflammable. Plunkett and his technician Jack Rebok had produced 100 pounds (45 kg) of tetrafluoroethylene gas (TFE), storing it in cylinders on dry ice. When the time came to use the material, nothing came out of the cylinder, even though it weighed the same as before. The gas had turned into a white powder. Plunkett and others at DuPont found that the substance was quite slippery and proved to be a good lubricant. It was resistant to chemicals and heat, and other substances would not adhere to it. The material was resistant to temperatures as high as 500°F (260°C). Plunkett and his colleagues more...

Man has cultivated the Earth for thousands of years, and for a large portion of that time he has been "tilling"—turning the soil to bury weeds and mix in fertilizer—in order to grow crops. Tillage, and agriculture in general, took a big step toward modern intensive processes when Australian inventor Arthur Clifford (Cliff) Howard (1893-1971) created the motorized tiller—the Howard Rotovator—in 1912. The son of a farmer, Howard studied engineering in Australia at Moss Vale, New South Wales. In 1912 he began experimenting on farming methods—primarily machines to improve tillage—on the family farm at Gilgandra, New South Wales. Howard noticed that regular plowing methods compacted the soil, making it more difficult to mix in fertilizer. Rotary tillage already existed, but was operated manually. Howard took a standard manual tiller and coupled it to his father's steam tractor. This proved superior to the standard plowing techniques, taking less effort to run, more...

Both waterproof and airtight, cellophane is now used for everything from food packaging to sticky tape. The man who invented it—Swiss textiles engineer Jacques E. Brandenberger (1872-1954)—initially wanted to develop a clear coating for cloth to make it waterproof after witnessing a wine spill on a restaurant tablecloth. He tried coating cloth with a thin sheet of viscose, but viscose made the cloth too stiff. The transparent sheet of film separated easily from the cloth and Brandenberger soon realized that the film itself had more potential than the waterproofed cloth. To create cellophane, Brandenberger dissolved cellulose fibers from materials such as celery, wood, cotton, or hemp in alkali and carbon disulfide to make viscose, which is then extruded through a slit into an acid bath to reconvert the viscose back into cellulose. The acid regenerates the cellulose, which forms a film, and further treatment—for example washing and bleaching—produces cellophane. (Rayon more...

Spectrophotometers are used to measure the intensity of electromagnetic radiation. Usually the measurements are confined by filters to a very narrow spectral range and the instrument is used to detect the change in brightness after the light radiation has either passed through a sample or been reflected off it. Early devices used the naked eye to determine the differences in intensity between two beams. Arthur Hardy (1895-1977), a physicist at the Massachusetts Institute of Technology, decided to replace the eye with the new cesium photocells, and thus detect intensities electronically. The plan was to produce a Spectrophotometer that automatically scanned through the visible spectrum and produced a pen-drawn spectrum showing how the light intensity varied with wavelength. Beam splitters and rotating polarizers were used and the two beams were compared by blinking quickly from one to another using a flicker photometer technique. Working in collaboration with the firm General Electric, more...

"What then is time? If no one asks me, I know what it is. If I wish to explain it, ...I do not know." Saint Augustine, theologian A time zone is a longitude band around the globe in which everyone sets their clocks to the same time— regulated by the movement of the sun. Before time zones were introduced, every town kept its own local time. But with the advent of the railways this system became very inconvenient, as the time at the starting point of a journey might well differ from the one at the terminus. In 1847 the railway companies in Great Britain recommended that all docks should be set using the same time marker. Noon on the Greenwich Meridian (0 degrees longitude) was chosen, which is known as Greenwich Mean Time (G.M.T.). Because Earth spins every twenty-four hours, local time varies by one hour for every 15-degree more...

Doctors treating polio patients found that while many sufferers were unable to breathe in the acute stage, when the action of the virus paralyzed muscles in the chest, those who survived this stage usually recovered completely. Such observations indicated the need to develop strategies to maintain respiration until the patient could breathe independently again. In 1927, chemical engineers Philip Drinker (1894-1972) and Louis Agassiz Shaw, from Harvard University, devised a tank respirator to maintain respiration. In the device, the patient's head stuck out of the end of the tank, with a sponge rubber seal to make it airtight. Air was then pumped from the tank to produce negative pressure causing the chest to expand and thus produce breathing. The first iron lung was installed in 1927 at Bellevue Hospital, New York, and in 1928 the first patient was an eight-year-old girl with polio, comatosed from lack of oxygen. One minute more...

"I... have [decided to call my invention] the Improved Endless-Wire-Rope Way." Andrew S. Hallidie The first cable-operated railway was the London and Blackwall Railway, which opened in 1840. It consisted of a line 3.5 miles (5.6 km) long with hemp rope hauling the cars, but because the ropes wore out too quickly, it switched to steam locomotives in 1848. In 1870 San Francisco attorney Benjamin Brooks proposed using cable cars to provide fast, inexpensive, and convenient access to the desirable heights of that hilly city. Horsedrawn cars worked well on level ground but had great difficulty with San Francisco's steep gradients. Brooks obtained a cable-line franchise from the city but was unable to obtain financing and sold it to Andrew Smith Hallidie (1836-1900). Hallidie had been the first person in California to manufacture wire rope, and by 1871 he had two cable- car patents to his name. He hired engineer more...

"Why have I stopped writing? I'd rather be a lightning rod than a seismograph..." Ken Kesey, writer During an earthquake the ground moves up and down and from side to side as a result of a release of energy from the Earth's crust. The seismograph is an instrument that continuously records this movement (seismic waves) as a function of time. Crude seismoscopes were invented by the Chinese around 132 C.E. but these merely indicated the direction of the earthquake's epicenter. Later Iranian and Italian instruments containing mercury baths that spilled in measured ways when the earthquake occurred indicated both direction of source and magnitude of movement, but not time of occurrence. British scientists Sir James Alfred Ewing, Thomas Gray, and John Milne (1850-1913) studied earthquakes and devices to record them whilst working in Japan. This resulted in the invention of Milne's horizontal pendulum seismograph in 1880. The idea of having more...

Paddle steamboats had been around for a century and propellers for half a century before the first proper motorboat took to the River Neckar near Stuttgart, Germany, in 1887. It had a petrol-driven internal combustion engine and was built by Gottlieb Daimler (1834-1900) and Wilhelm Maybach (1846-1929). Rumor had it that the two inventors were looking for a less risky vehicle for their new engine than the old stagecoach they had recently motorized. The 14.7 foot (4.5 m) long boat traveled at a maximum speed of 6 knots. Daimler practiced a mild deceit on his nervous first customers, by concealing the engine with a ceramic cover and informing them that it was "oil-electrical," which sounded a great deal safer than the potentially explosive petrol. The deceit clearly worked because the Neckar, as it was called, sold well. It was produced by the recently formed Daimler-Motoren-Gesellschaft (DMG), and sales were undoubtedly more...

A television system, by definition, transmits and receives live, moving half-tone images. Early versions, such as those invented by John Logie Baird in the 1920s, used crude, electromechanical, spinning, perforated, scanning discs to record and subsequently produce the images. The first transatlantic images were transmitted with this system in 1928. Television relies on the fact that the human brain can convert a sequence of slightly different still images into a moving picture if more than fifteen frames are received every second. As soon as the number drops below fifteen, the motion looks jerky. Today's televisions are a product of the invention of the cathode ray tube. This is coated with a phosphor that glows when an electron beam hits it. Behind the phosphor is a shadow mask that divides the image into picture elements (pixels). Television sets typically have 525 lines down the screen and these are raster scanned every more...