Tesla was delighted with the nature of X-rays because Roentgen's discovery had enabled seeing through an opaque material by means of fluorescent screen
and visualising metal objects, bones and calcareous shadows in every part of the body .
Televisions were originally fitted with cathode ray tubes, vacuum tubes containing one or more electron guns and a fluorescent screen
used to view images.
During one of his attempts, he happened to notice a green glow by a nearby fluorescent screen
; when he held his hand between it and the cathode-ray tube, he could see his bones and soft tissue.
The assistant then switched on the X-rays and you looked down two eye pieces to view the child's feet inside the shoes on a fluorescent screen
. All this to see whether the shoes fitted!
He created what he liked to call an "image dissector tube." It was a vacuum tube that could shoot streams of images and display them over a fluorescent screen
. When he showed his invention to his brother-in-law, the older man was astounded at what he saw.