Shortly after he had presented his first paper on x-rays to the physiomedical society at Würzburg, Roentgen found that x-rays do not emanate from the platinum of the anti-cathode only, but also from the walls of the glass tube, from the air which the rays penetrate, in fact that they fill every space in the room in which the Roentgen tube is operating. These secondary rays, as they are called, or diffused rays, as they should be called, affect the sensitized plate, and the blurred and flat negatives which we so often see must be ascribed to these unwelcome secondary rays.
Roentgen himself recommended lead diaphragms to be put between tube and body to annihilate the effect of the secondary rays, and an American investigator, Charles Finley Easton, was the first (1896) to cover his tubes with a lead shell into which a changeable opening was made. Rumpel, in Hamburg,
REICHMANN M. A MODIFICATION OF GOCHT'S COMPRESSION DIAPHRAGM.. JAMA. 1906;XLVI(17):1285. doi:10.1001/jama.1906.62510440039003a