Model of metal bodied end window Geiger-Muller tube, made by staff at 20th Century Electronics. Invented in 1928 by Geiger and Muller, this tube showed that, by stretching a high-voltage wire down its centre with a suitable gas filling, a counter could be made which was sensitive to beta-rays throughout its volume. A valve amplifier is usually attached to amplify the weak primary discharge. Made by 20th Century Electronics Ltd 1950-70. The model was made for, and presented to, Gilbert Tomes by his workforce at 20th Century Electronics (Later Centronic Ltd)