The first still images transmitted electrically were sent by early mechanical fax machines. In 1846, Scottish inventor Alexander Bain worked on chemical mechanical facsimile type devices and in 1846 was able to reproduce graphic signs in lab experiments. 
Frederick Bakewell made several improvements on Bain's design and demonstrated his device at the 1851 Great Exhibition in London. However, Bain and Bakewell's systems were rudimentary and produced poor quality images. They lacked synchronization between the transmitting mechanism and the receiving mechanism.
In 1861, the first practical operational electro-mechanical commercially exploited telefax machine, the Pantelegraph, was invented by the Italian physicist Giovanni Caselli. He introduced the first commercial telefax service between Paris and Lyon in 1865.
In 1873 two English telegraph engineers, Joseph May and Willoughby Smith, while investigating materials for use in the transatlantic cable, discovered that a selenium wire changed its electrical conductivity when exposed to light. This provided the basis for changing light into an electric signal. Thus is discovered the means to transform images into electric signals since the photoconductivity of selenium varies linearly with light intensity. Selenium will become the basis for the manufacture of photoelectric cells. 
The concept of electrically powered transmission of television images in motion was first sketched in 1878 as the telephonoscope, shortly after the invention of the telephone, in science fiction works.
On December 1, 1880 French publication "La Lumière électrique", published an article by Maurice Leblanc in which Leblanc outlined five functions required for a television system that formed the basis of all subsequent modern television systems.
However, Leblanc was not able to construct a practical working machine.
Paul Gottlieb Nipkow, a German engineer who invented the scanning disk in 1884 took television development to the next stage.
In 1883, while still a student he conceived the idea of using a spiral-perforated disk to divide a picture into a mosaic of points and lines.
He applied to the imperial patent office in Berlin for a patent covering an electric telescope for the electric reproduction of illuminating objects, in the category "electric apparatuses". This was granted on 15 January 1885, retroactive to 6 January 1884. (http://histv2.free.fr...)
Nipkow’s proposed system was the first electromechanical television system which employed a scanning disk at the transmission station - a spinning disk (by an electrical motor) with a series of holes spiraling toward the center, for rasterization (conversion of an image into points). The holes were spaced at equal angular intervals such that in a single rotation the disk would allow light to pass through each hole and onto a light-sensitive selenium sensor which produced the electrical pulses according to the light intensity coming from the transmitted object or image. Each hole, of the scanning disk captured a horizontal "slice" of the whole image. One complete revolution of the disk would provide a complete picture, or scan of the subject. The electrical pulses were sent to the receiver station by some communication means like a telegraph or telephone line. At the receiver end the inverted process took place. The arriving varying electrical signals were converted by a gas-discharge lamp (neon) into differing light intensities accordingly and again the light passed through a similar synchronously rotating (at the same speed) perforated scanning disk and the picture was reconstructed on a projection screen.
It is not known whether Nipkow ever attempted a practical realization of his disk but one may assume that he himself never constructed one. Nipkow's design would not be practical until advances in amplifier tube technology became available (1907) and the neon bulb of his time would generate enough light to make a bright clear picture. The device probably could have been only useful for transmitting still images over telegraph or telephone lines. 
Nipkow recounted his first sight of television at a Berlin radio show in 1928: "the televisions stood in dark cells. Hundreds stood and waited patiently for the moment at which they would see television for the first time. I waited among them, growing ever more nervous. Now for the first time I would see what I had devised 45 years ago. Finally I reached the front row; a dark cloth was pushed to the side, and I saw before me a flickering image, not easy to discern." The system demonstrated was from John Logie Baird's Baird Television Company. 
To sum it up: Paul Nipkow's scanning disk constituted the first TV camera and monitor ideas using the scanning principle, though not practical because of technical limitations of the time.
Nipkow’s concept was eventually (when technology enabled) used by John Logie Baird in Britain and by Charles Francis Jenkins in the United States to build the world's first successful televisions. In 1922 Jenkins sent a still picture by radio waves, and in 1923 moving silhouette images but the first true television success, the transmission of a live human face, was achieved by Baird in 1925. Unlike later electronic systems with several hundred lines of resolution, Baird's vertically scanned image, using a scanning disk embedded with a double spiral of lenses (in the holes), had only 30 lines, just enough to reproduce a recognizable human face.
Because only a limited number of holes could be made in the disks, and disks beyond a certain diameter became impractical, image resolution on mechanical television broadcasts was relatively low, ranging from about 30 lines up to 120 or so. Nevertheless, the image quality of 30-line transmissions steadily improved with technical advances, and by 1933 the UK broadcasts using the Baird system were remarkably clear. A few systems ranging into the 200-line region also went on the air a few years later. The "Televisor" as Baird has named his apparatus was alive.
Baird demonstrated the world's first colour transmission on 3 July 1928, using scanning discs at the transmitting and receiving ends with three spirals of apertures, each spiral with a filter of a different primary colour; and three colour light sources at the receiving end, with a commutator (switch) to alternate their illumination. Baird also made the world's first color broadcast on February 4, 1938, sending a mechanically scanned 120-line image from Baird's Crystal Palace studios to a projection screen at London's Dominion Theatre.
In 1927, his television was demonstrated over 438 miles of telephone line between London and Glasgow, and he formed the Baird Television Development Company (BTDC). In 1928, his company transmitted the first transatlantic television broadcast between London and New York.
In 1928 he also demonstrated stereoscopic television.
By 1939 the flickering and poor resolution image of the mechanical television concept was replaced completely by the full electronic more advanced TV systems. From 1936 to 1939 those two types of television coexisted together on the broadcasting market.
Although Baird had invested in the mechanical TV system in order to achieve early results, he had also been exploring electronic systems from an early stage and made many contributions to the field of electronic television after mechanical systems had taken a back seat. On August 16, 1944, John Logie Baird gave the first demonstration of a fully electronic color picture tube. His 600-line color system used triple interlacing, using six scans to build each picture.
Baird will be remembered as the first person to demonstrate a working television system which revolutionized our life in many aspects. (http://www.bairdtelevision.com)
Topics of Interest
Mechanical television (also called "Televisor") was a television system that used mechanical or electromechanical devices to capture and display images. However, the images themselves were usually transmitted electronically and via radio waves. The reason for the dual nature of mechanical television lay in the history of technology. The earliest mechanical television components originated with 19th century inventors, with 20th century inventors later adding electronic components as they were created. Mechanical systems were used in television broadcasting from 1928 to 1939, overlapping the all-electronic era by three years.
Instead of a Nipkow disk, mechanical television also used several other technologies - other arrangements often made use of a rotating drum, either with holes or with a series of mirrors on it.
Apart from the aforementioned mechanical television, which never took off for the practical reasons mentioned above, a Nipkow disk is used today in one type of confocal microscope, a powerful optical microscope. It is also sometimes used in the field of high speed photography, although in miniaturised and very high speed versions.
The advancement of all-electronic television (including image dissectors and other camera tubes and cathode ray tubes for the reproducer) marked the beginning of the end for mechanical systems as the dominant form of television. All-electronic television, first demonstrated publicly by Philo Farnsworth in 1934, and first used for broadcasting in 1936, was quickly advancing reaching 400 to more than 600 lines with fast field scan rates in the next few decades. The last mechanical television broadcasts ended in 1939.
Inventors attempted to build electronic television systems, based on the cathode ray tube, early as 1907 independently by English inventor A.A. Campbell-Swinton and Russian scientist Boris Rosing, but with no success.
By the late 1920s, when electromechanical television was still being introduced, several inventors were already working separately on practical versions of all-electronic transmitting tubes, including Philo Farnsworth (image dissector tube camera) and Vladimir Zworykin (Iconoscope camera) in the United States, and Kálmán Tihanyi in Hungary (Radioskop).
The word television itself had been coined by a Frenchman, Constantin Perskyi, at the 1900 Paris Exhibition or by Hugo Gernsback. The meaning of the word "television" comes from Greek "tele" - far and from Latin "visio" - vision; and together "television" means "far sight".
Build a Nipkow Scanning Disk
20=lens that intensify the light (by 19) reflected from the transmitted object
21=the transmitted object light reflection (cross) passing a framing mask
22=spiral lenses mounted on a rotating disc for scanning the object
14=other possible scanning disk arrangements for different radiations or needs
23=photoelectric cell (selenium) for infrared light detection
24=line amplifier transmitting amplified electrical signals from the cell to the receiver
25=gas-discharge lamp (neon), converts the arriving varying electrical signals into light
26=a rotaing disc for the detection of the arriving image
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Edison Thomas 2
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Galileo Galilei 2
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