When was the fax machine invented?

The FAX machine as we know it is an outgrowth of wire photo machines of 1920's and 1930's. Same principle. After that was weather fax which is also sent by shortwave to ships today. In all these an original drawing (weather map, newspaper, etc. or a B/W photo) was set on a drum. This was sent to spinning and a tightly focused beam of light was aimed at the item at one end. A synchronizing signal (usually based on 60 Hz power line frequency) was sent and then the light was moved down as the drum was spun, using gears that made picture scan in a fixed speed. A TV picture is produced in a similar but much faster method - the lines are painted across screen then moved down and across, etc. by a beam of electrons hitting the florescent screen. On the old style FAX (facsimile transmission) the light reflected off the paper and hit a photo cell. This generated a weak electric signal - more if white area was lit, less if dark area was lit. This was amplified and was caused to modulate at one. This was decoded at end and drove a lamp that was aimed at photo paper or sensitive flimsy thermal paper or a stylus and carbon paper to reproduce the image.

Flat bed scanners of today have the light fixed side to side, but moves down the paper to give best light where the pickup photodiode is scanning at the moment. The paper orig. document is fixed, while the photo cell is moved and scanned. The light/dark areas produce more or less light and this is converted to digital number stream, which then modulates a multi-tone modem and off it goes down the phone line. The earliest FAX like device was developed soon after the vacuum tube was invented and became generally available in the 1920's.

I have read of crude, experimental devices in lab work even earlier. This was just before the earliest crude TV system was developed (separately) by Dr. Lee De Forest (the inventor of the first amplifying vacuum tube - the triode - which enabled the entire electronics world; his last lab assistant was one of my mentors) and Philo Farnsworth out in the High Plains (ND?) in the 20's and early 30's. TV was broadcast in late 30's in a very limited way around NYC and a few large cities just before WW2. Radio, radar and electronics advances in WW2 brought the explosion of TV as we know it in early 50's.

Here are more opinions and answers from other FAQ Farmers:

Actually, the first fax machine was invented in 1842 by Alexander Bain who patented it in 1843. It consisted of a pendulum moving across that created an electric signal to another pendulm in sync with the first one that transmitted the signal to chemically treated paper.