Who Invented the Refrigerator

Refrigerators are an essential part of every modern kitchen. While just about every home makes use of a refrigerator, most consumers know nothing about the history of refrigeration and the invention of the refrigerator. The gradual creation of the modern refrigerator actually spans a process that began in the 18th century and culminated with the work of German engineer Carl von Linden in 1876.

The first efforts that eventually led to the modern refrigeration process that continues to form the basis for the fridges that grace kitchens all over the world today. William Cullen of the University of Glasgow first developed a process to create an artificial cooling medium in 1748. At the time, there did not appear to be much interest in applying the medium to use in commercial or home applications, so the process created little in the way of interest beyond the scientific community. It would take the better part of a century before someone would apply the basic principles discovered by Cullen and create a design for a refrigerating machine. 

Created in 1804, the design was the work of an American inventor by the name of Oliver Evans. However, no working prototype appeared until 1834. At that time, Jacob Perkins built a refrigeration machine that is often thought to be the forerunner of the modern refrigerator. A decade later, John Gorrie designed what is thought to be the first practical refrigerator. In 1844, Gorrie, a physician in the United State, constructed a working unit based on the design of Oliver Evans. Gorrie created the unit as a means of cooling the air in facilities he set aside for patients who were diagnosed with yellow fever. Many people credit Gorrie as being the individual who for all practical intents and purposes invented the refrigerator. 

Carl von Linden discovered and patented an improved method of liquefying gas in 1876, which made the process of manufacturing refrigerator models practical. Making use of such gases as ammonia, sulfur dioxide and methyl chloride, the new process formed the standard for cooling agents until the late 1920’s. By then, a number of accidents related to the use of these substances as cooling agents convinced manufacturers that a more stable element was needed. This effort led to the development of freon, which provided the standard for cooling agents for the bulk of the remainder of the 20th century, until the substance was leaked to damage to the ozone layer. 

From the simple working model created by John Gorrie in 1844 to the modern fridge units of today, the refrigerator has become one of the appliances that is an integral part of our lives. From storing our favorite foods to providing refreshing ice, the refrigerator is one device that most of us would not want to live without.

How Does a Television Work

A television produces a series of tiny dots on a screen that, when seen as a whole, appear as an image. Older televisions rely on a cathode-ray tube to produce images, and operate with an analog signal. As technology has advanced and broadcast signals transitioned from analog to digital, plasma and LCD (liquid crystal display) televisions were created. These TVs are more compact and have crisper pictures than their cathode-ray counterparts because they use a thin grid of pixels to create images rather than a vacuum tube.

The Eyes and the Brain

Most kinds of television work from the same basic principle. The tiny dots of light produced on the TV screen, called pixels, flash according to a specific pattern provided by the video signal. A person's eyes transmit this pattern to the brain, where it is interpreted as a recognizable image. The television set refreshes these patterns hundreds of times per second — faster than the human eye can see — which gives the illusion of movement.

The Cathode-Ray Tube

The cathode-ray tube (CRT), the oldest version of the television, consists of a vacuum tube with a narrow end and a wide end. The narrow end contains an ion gun, which shoots out a series of charged particles of electricity. A series of electromagnets guide the particles to specific points on the wide end of the tube, the screen that viewers look at. Phosphors, substances that light up when a charged electrical particle hits them, coat the screen's inner surface. The ion gun essentially sprays the image at the screen, much like a paint gun sprays paint onto a surface.

Different kinds of phosphors produce different colors, but for color television, only red, blue, and green are needed. Using these colors in various combinations and intensities can create all the colors the human eye can see. As energy travels from the ion gun to the phosphors, it is filtered to strike the exact point on the screen needed to produce a specific hue. In combination, all of these colored pixels create a color image.

Cathode-ray tubes are quite heavy due to the large amount of glass they contain, and relatively inefficient, especially when used in large-screen televisions. For this reason, new technologies were developed to make lighter sets with crisper images. In addition, the development of high definition (HD) digital broadcast signals made bigger screens more popular since the images were of higher quality. Plasma and LCD televisions were created in response.

The Plasma Screen

A plasma screen television consists of a number of tiny cells filled with neon and xenon gases. Each cell is linked to an electrode, which, when fired, excites the gases contained in the cell. The gases emit charge particles, much like the ion gun, that interact with phosphors coating the glass inside each cell. The phosphors light up, creating the image seen on the television screen. The large number of cells in a plasma screen makes for a great number of pixels, rendering a clearer and brighter image.

Compared to other technologies, plasma TVs produce some of deepest blacks, which means that the contrast ratio is very high. They also have very high refresh rates, so images with a lot of motion don't blur as they can on other televisions. If the image remains static, however, it can burn into the screen, creating a permanent discoloration; this is more common in older plasma TVs, and can also occur with CRT screens. Plasma screens can be set to be very bright, which requires a lot of electricity. They also tend to be thicker than LCD televisions, although much thinner than CRTs.

The LCD Screen

LCD televisions also use cells to create images. Rather than exciting gases as plasma TVs do, however, the cells contain a set of red, blue, and green filters covered by a layer of liquid crystals sandwiched between two pieces of glass. Depending on the display type, each cell is linked to either electrodes or thin film transistors (TFT), which trigger the necessary cells to create the image. A backlight — most often cold-cathode fluorescent lamp — lights up the screen so the image can be seen.

While LCDs are very light and thin, they are subject to "dead" pixels, where one or more cells on the screen do not change. Viewing LCD screens from an angle can also lower the picture quality. They have slower response times than plasma or CRT televisions as well, so images can "ghost" or blur in movement.

More recent versions of the LCD television use light-emitting diodes (LEDs) as the light source rather than cold-cathode fluorescent lamps. LED televisions require less electricity than regular LCD screens, and take up even less space. Also, LEDs generally emit a brighter white light, making these screens especially vivid.