Figure 1-1 Sketch of the Crookes' partial vacuum tube.
WILLIAM HITTORF (1880)
In 1880, William Hittorf found that a solid body placed between the cathode and
the area in which phosphorescence appeared, seemed to cast a shadow on the walls of
the tube. He, thus, concluded that cathode rays appeared to travel in straight lines and
could be easily stopped.
1-10. PHILLIPPE LENARD (1893)
a. In 1893, the French physicist, Phillippe Lenard investigated the penetrating
power of cathode rays. His observations led him to the conclusion that the rays could
be made to pass through very thin metal sheets. He discovered that cathode rays left
an impression on a photographic plate, much like a beam of light.
b. Lenard was the first to correctly describe the photoelectric effect of ultraviolet
light on metal. Additionally, he was the first scientist to measure the ionization potential
of the cathode rays.