John Logie Baird, the son of a Helensburgh minister, was an irrepressible inventor from a young age, starting with a telephone exchange that cut the electricity supply to Helensburgh, and later bringing electric light to the oil-lit manse. He first conceived the notion of television in 1903, when he was about fifteen, but it was not until he was in his thirties that he had the time to devote to experimenting. Prior to that his most successful innovation had been heated socks. Using a collection of scrap materials, and working from a garret in London, he finally succeeded in transmitting the first televized images.
In spite of every effort … I could not get anything like enough light to operate the photoelectric cells available and I decided to try either to make a new cell or to find some way of using the selective selenium cell. Two devices sensitive to light were known, the selenium cell and the photoelectric cell. The photoelectric cell of those days was so extremely insensitive to light that no detectable signals could be got from it, except by shining a powerful light directly into it. It could be used to show the difference between total darkness and the light from a powerful arc lamp beam, so that it was possible by interposing simple shapes in the path of an arc lamp beam, to send their shadows; but to use it for true television where all the light available would be relatively infinitesimal light thrown back from, say, a human face, was utterly out of the question.
The selenium cell was enormously more sensitive, but it had what all writers on the subject agreed was an insurmountable objection to its use – a time lag; that is it took some little time to respond to light.
I made a number of efforts to increase the sensitivity of the photoelectric cells and to find other materials which would give greater reactions to light. The light sensitivity of the human eye, according to Eldridge, Green and certain others, resides in a purple fluid found in the retina of the eye, and called the visual purple.
I decided to make an experimental cell using this substance, and called at the Charing Cross Ophthalmic Hospital, and asked to see the chief surgeon. I told him I wanted an eye for some research work I was doing on visual purple. He thought I was a doctor and was very helpful.
‘You’ve come at an appropriate time,’ he said, ‘I am just taking out an eye, and will let you have it, if you will take a seat until the operation is over.’
I was handed an eye wrapped in cotton wool – a gruesome object. I made a crude effort to dissect this with a razor, but gave it up and threw the whole mess into the canal. My efforts to produce a sensitive cell without time lag proving abortive, I decided to try selenium cells and see what could be done – if anything – to overcome the time lag. The first thing I tried was to use interrupted light, by passing the light rays through a serrated disc, which acted as a light chopper. The time lag did not enter into the matter. The cell had to distinguish only between interruptions and no interruptions. With this I could use selenium but the light chopper split the picture into crude bars, so nothing could be sent but coarse outlines. I discarded the chopper and concentrated on the problem of overcoming the time lag.
I used, as the object for my experimental transmission, a ventriloquist’s dummy’s head. This came out on the screen as a streaky blob. What was happening was this: When the light fell on the cell, the current, instead of jumping instantly to its full value, rose slowly and continued rising as long as the light fell on it. Then when the light was cut off the current did not stop instantly, but only stopped increasing and began falling, taking an appreciable time to get to zero. While watching this effect, it occurred to me that it could be cured or mitigated if I superimposed a curve representing the rate of change of the current with time upon the curve of current with time.
By putting a transformer in the circuit I could, in effect, accomplish this. The moment the light fell upon the cell there would be a change from no current to current. And although the current would be small the rate of change would be great; again at the time when the current changed from increasing to decreasing, the rate of change would be maximum, so that I would get a big up kick and a big down kick when required. My amplifier was a DC battery coupled amplifier (and a source of infinite worry). Now I decided to build a second amplifier, battery coupled but with one transformer coupled stage, so that one amplifier could give me the time/current curve, and the second the time/rate of current curve. I would then mix the two until the time lag was corrected. And this I proceeded to do. I was on the right track.
Funds were going down, the situation was becoming desperate and we were down to our last £30 when at last, one Friday in the first week of October 1925, everything functioned properly. The image of the dummy’s head formed itself on the screen with what appeared to me almost unbelievable clarity. I had got it! I could scarcely believe my eyes, and felt myself shaking with excitement.
I ran down the little flight of stairs to Mr Cross’s office and seized by the arm his office boy William Taynton, hauled him upstairs and put him in front of the transmitter. I then went to the receiver only to find the screen a blank. William did not like the lights and the whirring discs and had withdrawn out of range. I gave him 2/6 and pushed his head into position. This time he came through and on the screen I saw the flickering, but clearly recognizable, image of William’s face – the first face seen by television – and he had to be bribed with 2/6 for the privilege of achieving this distinction.