In 1873 Joseph May, a telegraph operator discovered the first step towards the transmission of pictures. He found that the electrical resistance of selenium bars varied in proportion to the intensity of light to which they were exposed. This was called the “photoelectric effect”. The basic concept was that light signals could be converted into electric signals and transmitted from one location to others. This conversion allowed the signals to be transmitted in electric form from one location before being returned to the original light patterns at the receiving end. A sequence of pictures sent in this way could provide the basis for a television system. However making a working system was practically impossible at that time. In 1875 George Carey proposed using a system where all points in an image were simultaneously scanned and transmitted. The huge number of cells and bulbs required for reasonable quality pictures made this impossible to implement (due to lack of the required technologies). Constantin Senlecq in 1881 came up with a more feasible idea. This involved converting the image into a number of elements or packets and then transmitting these in a series. This is the basic concept behind all of today’s television systems.
The scanning system was designed by Paul Nipkow in 1884. This system consisted of a spinning disk at either end of transmission. If the receiving disk is spun at the same rate as the transmitting disk, a picture could be reproduced. The problem that cropped up was that the selenium photoelectric cells were too slow to react to changes in light intensity and amplifiers did not exist to amplify the weak signals.
During the 1870's Sir William Crookes conceived and created a vacuum tube, which produced a beam of electrons. This tube was known simply as 'The Crookes Tube'. By the turn of the century this tube had evolved into the Cathode Ray Tube in which a beam of electrons was deflected through horizontal and vertical electromagnets onto a fluorescent screen. This Cathode Ray Tube or CRT as it is commonly know as is the most important component of all television sets.
In 1907 experiments were conducted into its use as a receiver screen for television. And in 1911 A Cambell Swinton suggested making use of the cathode ray tube to produce the worlds first television system. Unfortunately, technology was still insufficient for the demands of such a system. The advent of the faster potassium photoelectric cell and the neon lamp (which allowed rapid variation in light intensity) allowed the mechanical system to become a reality. In 1925, John Logie Baird, a Scottish engineer displayed a simple working system and subsequently he was able to demonstrate the first transmission of a real picture; a person’s head, scanned in 30 lines and at 5 frames per second. The world had just been “televised”. The scanning process involved the use of a spinning disk with a spiral pattern of holes around the outer edge as suggested by Nipkow.
